Response to Suter and NIOSH Robert A. Dobie1 and William W. Clark2 We thank Suter and Morata et al. for their letters. The authors of Morata et al. are all employees of the National Institute for Occupational Safety and Health (NIOSH); it is our understanding that their letter, lacking the disclaimer usually attached to public comments of federal employees, represents the official position of that agency, and thus, we will refer to it as the NIOSH letter. We will address each of the comments in the Suter and NIOSH letters, followed by a brief discussion on important issues that they omitted. Although we would have preferred a brief response, the extent, nature, and scientific foundation of the arguments brought forward require a thorough rebuttal. Suter and NIOSH are longtime collaborators and proponents of the 3-dB exchange rate (ER), so their disagreement with our article is not unexpected. What was unexpected was NIOSH’s assertion that a “re-examination of the exchange rate” requires adherence to a long list of criteria, including the use of two raters of study quality, with a third to adjudicate conflicts; a formal assessment of quality across multiple domains; attempting to contact authors; presenting study findings grouped by “certainty of exposure level estimates”; an evaluation of the risk of bias; and others. We disagree and note that neither NIOSH (1998) nor Suter’s (1992) report to NIOSH considered any of these elements when they re-examined the 5-dB ER, which NIOSH (1972) had previously recommended, and decided to instead advocate for the 3-dB ER. For those who have not read our article, we reviewed all the literature we could find that could shed light on the issue of the appropriate ER, based on human noise-induced permanent threshold shift (NIPTS). We included every study that had been cited by Suter (1992) and NIOSH (1998), as well as other studies from the reference lists of those articles, and additional studies discovered by a literature search. We applied clear inclusion criteria, analyzed included studies in comparison with the predictions of an international standard (International Organization for Standardization [ISO]-1999, 1990) using fully transparent methodology that others can replicate, and submitted our work to a peer-reviewed journal. We believe that our contribution was unique in this literature. We could not replicate the findings of a frequently cited previous review (Passchier-Vermeer 1973) that despite its unclear methodology and lack of peer review has been very influential (as we note later). Although we reviewed 19 studies in detail and included nine in our summary table, it is notable that neither Suter nor NIOSH question any of our exclusions, nor do they suggest alternative interpretations for any of the included studies. Suter notes that we “excluded most of the studies used by Passchier-Vermeer from their analysis.” That is misleading: we read, analyzed, and commented on all the studies
Passchier-Vermeer relied on and explained why most of them had to be excluded from our final summary table. Some studies that NIOSH now considers of questionable quality (Holmgren et al. 1971; Johansson et al. 1973; Thierry et al. 1978) were explicitly cited by NIOSH (1998) and Suter (1992) without any critique of study quality. For these three and a fourth (NIOSH 1982), NIOSH argues that we did not adhere to our own inclusion criteria because both exposure metrics (time-weighted average, and the equal-energy average or LAeq8h) could not be estimated. A careful reading of our article would have shown that the relevant criterion was not that both could be estimated but rather that one could be estimated and the other would be expected to differ by at least 1 dB. In all these cases, this criterion was met. Regarding Martin et al. (1975), we reported that their electric furnace subgroup had a timeweighted average/LAeq8h difference of 2 dB, thus meeting our inclusion criteria. For Sataloff et al. (1969), we clearly indicated our assumption that the miners had begun their work at age 20 years. Stephenson et al. (2010) made the identical assumption in their analysis of data from a U.S. Army hearing conservation program (HCP). To summarize, we applied our inclusion criteria uniformly and made our assumptions explicit. Suter claims that 82% of Sataloff’s miners used hearing protection devices (HPDs) regularly, but the cited article does not say that. As we acknowledged, Sataloff et al. stated that the miners had had some use of HPDs, after many years of unprotected exposure. In addition, Sataloff et al. found no difference in hearing thresholds between (occasional) users and nonusers of HPDs. NIOSH states (and we agree) that searching Medline alone is not “sufficient for a systematic review,” implying that we did only that. However, a careful reading of our article would have shown that we went far beyond a Medline search. For example, we asked multiple other colleagues, including Suter and one of the NIOSH authors (Murphy), to point us to publications other than the ones we had already found. NIOSH’s comment that we ignored “gray literature” and examined only peer-reviewed literature is surprising because our analysis included two reports by their own agency (NIOSH 1976, 1982) that were not published in peer-reviewed journals and would be considered “gray literature.” NIOSH objects to our use of the binomial sign test because the six different studies might not have been statistically independent. However, these studies were reported by different and nonoverlapping author groups, in different sites and different years, with nonoverlapping subject groups. Thus, it is difficult to see how their independence can be doubted. The six studies were not, of course, randomly selected (they were the entire known population of such studies); random selection is appropriate only when the entire population is too large to conveniently study. Their third objection is of course valid: if one of the six studies had favored the 3-dB rather than the 5-dB ER, the sign test would not have been statistically significant. That
University of Texas Health Science Center, San Antonio, Texas, USA; and 2Program in Audiology and Communication Sciences, Washington University School of Medicine, St. Louis, Missouri, USA.
1
0196/0202/2015/364-0492/0 • Ear & Hearing • Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved • Printed in the U.S.A. 492
LETTER TO THE EDITOR
is why we characterized this result as only suggestive of a nonrandom outcome. NIOSH questions the “suitability” of re-examining the human NIPTS data, “excluding robust animal studies and temporary threshold shift [TTS] studies” that also address the ER issue. We clearly indicated in our article that all three of these study types can shed light on the ER issue and should be of interest to regulatory agencies. We also cited reviews of animal permanent threshold shift and human TTS data that would support the 3-dB ER only for brief uninterrupted exposures. NIOSH now considers the available human NIPTS data to be based on “outdated methodologies” (presumably the lack of modern dosimetry); but NIOSH (1998) considered these data not only worthy of discussion but also supportive of their recommendation of a 3-dB ER. To arrive at that conclusion, both NIOSH and Suter (1992) relied heavily on Passchier-Vermeer’s (1973) nonpeer-reviewed synthesis of 11 studies of human NIPTS, with no mention of most of the individual studies. Our approach was to review each of these 11 papers and other relevant studies; this was no small task because several of the studies required translation before we could read them. We concluded that the human NIPTS data do not support the 3-dB ER. NIOSH assumes that sound level measurements made before about 1980 would have overpredicted hearing loss (in other words, sound level readings would have been too high). However, neither of their cited references (two abstracts by Earshen 1980, 1994) suggests systematic overestimation of exposure by earlier sound level measurements. We clearly indicated in our paper that hazard estimates for exposures rich in impact or impulse noise might require additional considerations, such as the measurement of kurtosis. Although we disagree with NIOSH’s assertion that these alternative metrics have been demonstrated to be more accurate, that discussion is outside the scope of our article. Incidentally, one of the articles they cite regarding kurtosis (Lataye & Campo 1996) does not mention kurtosis and shows (in chinchillas) that the 5-dB ER predicted NIPTS better than the 3-dB ER for most of their noise exposures. The NIOSH and Suter letters rely extensively on endorsements from professional and governmental organizations, implying that if enough such organizations support the 3-dB ER, the subject is closed. We hope that most readers agree with us that nothing in science can ever be immune to criticism and re-examination. We have read the position statements of most of the organizations they mention and find that with few if any exceptions, they have not reviewed primary literature other than the sources that we included in our article. Most of them rely directly or indirectly—as did Suter and NIOSH—on PasschierVermeer (1973), a synthesis that we believe to be unreliable. Others may support the 3-dB ER for a more defensible reason: a wish to be overprotective in regulation (many employers require everyone in areas where average levels exceed 85 dBA to wear HPDs; this rule, equivalent to a zero-dB ER, is clearly overprotective for people passing through briefly but might be justified on the basis of simplicity and enforceability). As we acknowledged, the 5-dB ER could be more accurate for most exposures but still might underpredict hazard for some exposures, such as brief uninterrupted exposures. In addition to Suter (1992) and NIOSH (1998), NIOSH cites four other papers that they claim addressed “the rationale for using the 3-dB exchange rate,” but none of these four reports
493
provides any new information that would support that ER. Prince et al (1997) used only the 5-dB ER to predict the hearing levels in their subjects, never suggested that it was inadequate, and never mentioned any other ER. Stephenson et al (2010) wrote a letter to the editor that simply cited other reviews and position statements. Murphy and Kardous (2012) was a NIOSH report limited to impulse and impact noise metrics, which is outside the scope of our article. Themann et al. (2013) was a NIOSH review that neither presented nor cited data supporting any ER. NIOSH objects to our focus on people with intermittent or fluctuating exposures as a “subgroup of workers who are least exposed to hazardous noise.” We found this surprising. First, hazard obviously depends on both noise level and duration. High-level intermittent noise can be more hazardous than continuous low-level noise. Second, assessing hazard for intermittent/fluctuating exposures is the main point of choosing an ER. For truly continuous 8-hr noise exposures, the ER does not matter! NIOSH claims that there is “overwhelming evidence that many workers in programs using this exchange rate [5-dB] are sustaining noise-induced hearing loss [NIHL]” and supports this by reference to “staggering information” from the Bureau of Labor Statistics (2013). The cited data show that about 11 of every 10,000 manufacturing workers had standard threshold shifts (STSs) recorded in 2012 (rates were much lower for all other industry sectors). There are many causes for STSs in HCPs, including age-related threshold shifts, audiometric testretest variability, headphone reversals during testing, and ear diseases, in addition to NIHL, which can be caused by occupational and/or nonoccupational exposures. STS cases caused by occupational noise can in turn be attributable to many factors, including employer failure to enforce regulations and employee failure to comply with the use of HPDs. NIOSH implies that the inadequacy of current OSHA regulations, including the use of the 5-dB ER, is the cause of these threshold shifts and states, “a more conservative exchange rate has the best potential to reduce noise exposures and the burden of noise-induced hearing loss.” We know of no evidence for these two positions, and NIOSH cites none. It is unclear to us how a change in the ER would motivate employers to implement better HCPs and to put more emphasis on noise control, or how including more workers in those programs would motivate workers to more faithfully use HPDs Seixas et al. (2005a, cited by Suter) compared different noise exposure metrics to each other but contained no hearing threshold data, did not evaluate the accuracy of these metrics in predicting noise-induced shifts, and thus appears to be irrelevant to the point being made in Suter’s letter. Perhaps Suter meant to cite Seixas et al. (2005b), which showed that after 3 years, construction apprentices had experienced changes in 4 kHz thresholds that were “extremely small, and not significantly different from zero.” Seixas et al. noted that the longitudinal shifts were less than predicted by the ISO-1999 model, using the 3-dB ER and that the intermittency of construction exposure was among the possible explanations for this discrepancy. They acknowledged that findings like this supported the 5-dB ER but suggested that other explanations were more plausible. Seixas et al. (2012) presented the 10-year longitudinal data for the same apprentice group and cautiously asserted that the “relatively small” mean threshold shifts at 4 kHz (2 to 3 dB per 10 dBA
494
LETTER TO THE EDITOR
exposure level increase) were “somewhat higher” than and “consistent with or exceeded” those predicted by the ISO-1999 model. Their analysis had two flaws that render this conclusion even more tenuous than they stated. First, the ISO model predicts median, not mean shifts; hearing threshold distributions are almost always positively skewed, such that means are higher than medians. Second, Seixas et al. assumed that the 12-dB mean threshold at baseline was entirely attributable to noise exposure before the onset of the study, and then used the model to generate an estimate of only 1 dB of additional shift for the next 10 years. Median 4 kHz threshold for U.S. men at age 30 yr is 7 dB (per Hoffman et al. 2010), and the mean would be higher; this might support an estimate of prior NIPTS of 5 dB or less (12 minus 7). With that assumption, the ISO model predicts that 10 yr of additional exposure at 87 dBA will yield an additional 3 dB or more of NIPTS (median, not mean). With these points taken into consideration, the threshold shifts experienced by these apprentices were either consistent with or less than those predicted by ISO-1999. We disagree with Suter’s interpretation of the data reported by Davis et al. (2012). These authors compared hearing thresholds predicted by ISO-1999 (based on a subject’s age, sex, and noise exposure) to their actual thresholds. Unfortunately, they made two important errors that biased their results. First, Davis et al. compared subjects’ binaural average thresholds to the better-ear thresholds in Annex B of ISO-1999 (1990). The underlying data in Annex B (Glorig & Roberts 1965) show that binaural average thresholds were 4 to 5 dB higher than better-ear thresholds, for the frequencies and age groups represented in Davis et al. (2012). Second, it appears that Davis et al. presented subject group median thresholds without making the 2.5-dB correction that is necessary before comparison with these Annex B medians, assuming that the medians had been calculated in the conventional way (Hoffman et al. 2010). In combination, these errors would make the differences between their subjects’ hearing and ISO-1999 predictions seem about 7 dB worse than they really were. Figure 2 in Davis et al. (2012) summarizes data for all their subjects; median thresholds appeared to be 1 to 8 dB worse than predicted. With appropriate corrections as indicated earlier, these differences would disappear. Suter states that ISO-1999 (1990) is based on data from Passchier-Vermeer (1973), as well as those of Baughn (1973); that is incorrect. The Passchier-Vermeer data that went into the development of ISO-1999 (1990) were not the intermittent/fluctuating noise data that were reviewed by us (Passchier-Vermeer 1973), but her data on people exposed to steady state noise (PasschierVermeer 1968). Neither the Baughn data nor the Passchier-Vermeer (1973) data were included in the ISO-1999 (1990) model, as explained by Johnson (1978, 1988), who created the model. Suter suggests that pure-tone thresholds may be an inadequate measure of NIHL, citing a study of cochlear nerve degeneration after TTS in mice (Kujawa & Liberman 2009). She also cites a finding of progressive hearing loss after a single noise exposure in adolescent mice (Kujawa & Liberman 2006). If these phenomena occur in humans, it seems unlikely that they would occur with exposures below the current OSHA exposure limits (and therefore the stricter exposure limits recommended by NIOSH would have no effect, at least with respect to these hypothetical problems in humans). The mouse exposures caused very large and persistent TTS (>40 dB, 24 hr later); TTS of that magnitude in humans would require an exposure well above the OSHA permissible limit.
The longitudinal studies that Suter cites to support the hypothesis of progressive noise-induced damage after the cessation of noise lack data on noise exposure (Gates et al. 2000) and statistical analysis (Rosenhall 2003). Many studies that include both noise exposure data and statistical analysis do not support this hypothesis (Rösler 1994; Lee et al. 2005; Cruickshanks et al. 2010; Albera et al. 2010; Hoffman 2015). Suter states that our comment that the essence of public policy decisions is balancing costs and benefits is a “misrepresentation of public policy.” We disagree. Her statement is based on a narrow reading of the language of the OSHA enabling legislation but does not consider almost 30 years of presidential executive orders. In 1982, President Reagan issued an executive order requiring agencies to use cost-benefit analysis (Exec. Order No. 12,291, 3 C.F.R. 127, 1982). Thus, in the final Hearing Conservation Amendment published in 1983, OSHA no longer claimed exemption from considering both costs and benefits. In 1994 President Clinton issued an order on the same topic, requiring agencies to include qualitative measures of costs and benefits (Exec. Order No. 12,866, 3 C.F.R. 638, 639, 1994). In 2011, President Obama issued Executive Order 13,563 requiring all federal regulations to “take into account benefits and costs, both quantitative and qualitative.” Our statement regarding costs and benefits was consistent with executive orders spanning three decades. Neither Suter nor NIOSH offered any alternative analysis of the 10 studies we excluded from our summary table, or of the nine studies we included in that table, that would support the 3-dB ER. Furthermore, neither Suter nor NIOSH presented any additional data supportive of the 3-dB ER (e.g., evidence that workers whose employers’ HCPs use the 3-dB ER experience less hearing loss than workers whose employers’ HCPs use the 5-dB ER). Their main position now appears to be that the human NIPTS data are unreliable and cannot be used to question the 3-dB ER (logically, that would mean that these data cannot be used to support the 3-dB ER, either). Our article recommended prospective longitudinal research that could provide better NIPTS data to address the ER, and NIOSH now agrees. As a federal agency with an annual research budget (2014) over $100 million, NIOSH could have funded studies on this type anytime in the 20 years since they began to advocate for the 3-dB ER (NIOSH 1995). We urge them to do so now. To summarize, we appreciate the interest of Suter and NIOSH in our article, but find their arguments unpersuasive. Many of their assertions are incorrect, and others are irrelevant, as described earlier. Although we disagree with many of their positions, we value the opportunity to participate in a full discussion of the many important issues in this area.
REFERENCES Albera, R., Lacilla, M., Piumetto, E., et al. (2010). Noise-induced hearing loss evolution: Influence of age and exposure to noise. Eur Arch Otorhinolaryngol, 267, 665–671. Baughn, W. L. (1973). Relation Between Daily Noise Exposure and Hearing Loss as Based on the Evaluation of 6835 Industrial Noise Exposure Cases. AMRL-TR-73 (AD 767 204). Wright-Patterson Air Force Base, OH: Aerospace Medical Research Laboratory. Bureau of Labor Statistics. (2013). Employer-Reported Workplace Injuries and Illnesses–2012. Washington, DC: Bureau of Labor Statistics, United States Department of Labor. Retrieved November 21, 2014, from http:// www.bls.gov/news.release/pdf/osh.pdf.
LETTER TO THE EDITOR
Cruickshanks, K. J., Nondahl, D. M., Tweed, T. S., et al. (2010). Education, occupation, noise exposure history and the 10-yr cumulative incidence of hearing impairment in older adults. Hear Res, 264, 3–9. Davis, R. I., Qiu, W., Heyer, N. J., et al. (2012). The use of the kurtosis metric in the evaluation of occupational hearing loss in workers in China: Implications for hearing risk assessment. Noise Health, 14, 330–342. Earshen, J. J. (1980). Noise dosimeters: On measurement reliability and instrument accuracy. J Acoust Soc Am, 68, S21–S21. Earshen, J. J. (1994). On comparing noise metrics applied to hearing conservation. J Acoust Soc Am, 96, 3272. Gates, G., Schmid, P., Kujawa, S., et al. (2000). Longitudinal threshold changes in older men with audiometric notches. Hearing Res, 141, 220–228. Glorig, A., & Roberts, J. (1965). National Center for Health Statistics: Hearing Levels of Adults by Age and Sex United States 1960–1962. Vital and Health Statistics, PHS Publication Number 1000 Series 11, No. 11. Washington, DC: Public Health Service, US Government Printing Office. Hoffman, H. J. (2015). Age-related hearing loss: Predicted age-specific incidences based on cross-sectional prevalences, compared with observed age-specific incidences from a longitudinal study. ARO Abstracts, 38, 190. Hoffman, H. J., Dobie, R. A., Ko, C. W., et al. (2010). Americans hear as well or better today compared with 40 years ago: Hearing threshold levels in the unscreened adult population of the United States, 1959-1962 and 1999-2004. Ear Hear, 31, 725–734. Holmgren, G., Johnsson, L., Kylin, B., et al. (1971). Noise and hearing of a population of forest workers. Br Ac Soc Spec, 1, 35–42. International Organization for Standardization. (1990). Acoustics: Determination of Occupational Noise Exposure and Estimation of Noise-Induced Hearing Impairment, ISO-1999. Geneva: International Organization for Standardization. Johansson, B., Kylin, B., Reopstorff, S. (1973). Evaluation of the hearing damage risk from intermittent noise according to the ISO recommendations. Proceedings of the International Congress on Noise as a Public Health Problem. EPA Report 550/9-73-008. Johnson, D. L. (1978). Derivation of Presbyacusis and Noise-Induced Permanent Threshold Shift (NIPTS) to Be Used for the Basis of a Standard on the Effects of Noise on Hearing. AMRL-TR-78-128. Wright-Patterson Air Force Base, OH: Armstrong Medical Research Laboratory. Johnson, D. L. (1988). Risk of hearing loss from noise. Semin Hear, 9, 279–284. Kujawa, S. G., & Liberman, M. C. (2006). Acceleration of age-related hearing loss by early noise exposure: Evidence of a misspent youth. J Neurosci, 26, 2115–2123. Kujawa, S. G., & Liberman, M. C. (2009). Adding insult to injury: Cochlear nerve degeneration after “temporary” noise-induced hearing loss. J Neurosci, 29, 14077–14085. Lataye, R., & Campo, P. (1996). Applicability of the L(eq) as a damage-risk criterion: An animal experiment. J Acoust Soc Am, 99, 1621–1632. Lee, F. S., Matthews, L. J., Dubno, J. R., et al. (2005). Longitudinal study of pure-tone thresholds in older persons. Ear Hear, 26, 1–11. Martin, R. H., Gibson, E. S., Lockington, J. N. (1975). Occupational hearing loss between 85 and 90 dBA. J Occup Med, 17, 13–18. Murphy, W. J., & Kardous, C. A. (2012). In-Depth Survey Report: A Case for Using A-Weighted Equivalent Energy as a Damage-Risk Criterion. Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, EPHB-350-11a. NIOSH. (1972). NIOSH Criteria for a Recommended Standard: Occupational Exposure to Noise. Cincinnati, OH: U.S. Department of Health, Education, and Welfare, Health Services and Mental Health
495
Administration, National Institute for Occupational Safety and Health, DHEW (NIOSH). Publication No. HSM 73-11001. NIOSH. (1976). Survey of Hearing Loss in the Coal Mining Industry. Cincinnati, OH: U.S. Department of Health, Education, and Welfare, Public Health Service, Center for Disease Control, National Institute for Occupational Safety and Health (NIOSH) Publication No. 76-172. NIOSH. (1982). Health Hazard Evaluation Report. Newburgh Fire Department, Newburgh, NY. Cincinnati OH: U.S. Department of Health and Human Services, Public Health Service, Center for Disease Control, National Institute for Occupational Safety and Health (NIOSH) Publication No. HETA 81–059–1045. NIOSH. (1995). Health Hazard Evaluation Report 95-0167-2539. The Western States Machine Company, Hamilton, Ohio. Cincinnati OH: U.S. Department of Health and Human Services, Public Health Service, Center for Disease Control, National Institute for Occupational Safety and Health, DHEW (NIOSH) Publication No. HETA 95-0167-2539. NIOSH. (1998). NIOSH Criteria for a Recommended Standard: Occupational Noise Exposure Revised Criteria 1998. Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control, National Institute for Occupational Safety and Health, DHHS. Publication No. 98–126. OSHA. (1983). Department of Labor Occupational Noise Exposure Standard. US Department of Labor, Occupational Safety and Health Administration, CFR29 (XVII) 1910.95. Passchier-Vermeer W. (1968). Hearing loss due to exposure to steady-state broadband noise. Report # 35, Institute for Public Health Eng. (sound and light division), The Netherlands. Passchier-Vermeer, W. (1973). Noise-induced hearing loss from exposure to intermittent and varying noise. In Proceedings of the International Congress on Noise as a Public Health Problem. EPA Report 550/9-73-008. Prince, M. M., Stayner, L. T., Smith, R. J., et al. (1997). A re-examination of risk estimates from the NIOSH Occupational Noise and Hearing Survey (ONHS). J Acoust Soc Am, 101, 950–963. Rosenhall, U. (2003). The influence of ageing on noise-induced hearing loss. Noise Health, 5, 47–53. Rösler, G. (1994). Progression of hearing loss caused by occupational noise. Scand Audiol, 23, 13–37. Sataloff, J., Vassallo, L., Menduke, H. (1969). Hearing loss from exposure to interrupted noise. Arch Environ Health, 18, 972–981. Seixas, N., Neitzel, R., Sheppard, L., et al. (2005a). Alternative metrics for noise exposure among construction workers. Ann Occup Hyg, 49, 493–502. Seixas, N. S., Goldman, B., Sheppard, L., et al. (2005b). Prospective noise induced changes to hearing among construction industry apprentices. Occup Environ Med, 62, 309–317. Seixas, N. S., Neitzel, R., Stover, B., et al. (2012). 10-Year prospective study of noise exposure and hearing damage among construction workers. Occup Environ Med, 69, 643–650. Stephenson, M. R., Byrne, D. C., Ohlin, D. W., et al. (2010). Perspectives on “Efficacy of the U.S. Army policy on hearing conservation programs.” Mil Med, 175, xii–xvi. Suter, A. H. (1992). The relationship of the exchange rate to noise-induced hearing loss. Report for the Doc. Development Branch, Div. of Standards Development and Technology Transfer, NIOSH, Public Health Service, U.S. Dept. of Health and Human Services. Themann, C., Suter, A. H., Stephenson, M. R. (2013). National Research Agenda for the Prevention of Occupational Hearing Loss—Part 1. Semin Hear, 34, 145–207. Thierry, L., Damongeot, A., Derzko, G., et al. (1978). Etude des risques auditifs auxquels sont soumis les salaries argricoles en exploitations forestieres et en scieries. Report for the Institut National de Recherche et de Securite (INRS), Vandoeuvere-Les-Nancy, France.
Passchier-Vermeer relied on and explained why most of them had to be excluded from our final summary table. Some studies that NIOSH now considers of questionable quality (Holmgren et al. 1971; Johansson et al. 1973; Thierry et al. 1978) were explicitly cited by NIOSH (1998) and Suter (1992) without any critique of study quality. For these three and a fourth (NIOSH 1982), NIOSH argues that we did not adhere to our own inclusion criteria because both exposure metrics (time-weighted average, and the equal-energy average or LAeq8h) could not be estimated. A careful reading of our article would have shown that the relevant criterion was not that both could be estimated but rather that one could be estimated and the other would be expected to differ by at least 1 dB. In all these cases, this criterion was met. Regarding Martin et al. (1975), we reported that their electric furnace subgroup had a timeweighted average/LAeq8h difference of 2 dB, thus meeting our inclusion criteria. For Sataloff et al. (1969), we clearly indicated our assumption that the miners had begun their work at age 20 years. Stephenson et al. (2010) made the identical assumption in their analysis of data from a U.S. Army hearing conservation program (HCP). To summarize, we applied our inclusion criteria uniformly and made our assumptions explicit. Suter claims that 82% of Sataloff’s miners used hearing protection devices (HPDs) regularly, but the cited article does not say that. As we acknowledged, Sataloff et al. stated that the miners had had some use of HPDs, after many years of unprotected exposure. In addition, Sataloff et al. found no difference in hearing thresholds between (occasional) users and nonusers of HPDs. NIOSH states (and we agree) that searching Medline alone is not “sufficient for a systematic review,” implying that we did only that. However, a careful reading of our article would have shown that we went far beyond a Medline search. For example, we asked multiple other colleagues, including Suter and one of the NIOSH authors (Murphy), to point us to publications other than the ones we had already found. NIOSH’s comment that we ignored “gray literature” and examined only peer-reviewed literature is surprising because our analysis included two reports by their own agency (NIOSH 1976, 1982) that were not published in peer-reviewed journals and would be considered “gray literature.” NIOSH objects to our use of the binomial sign test because the six different studies might not have been statistically independent. However, these studies were reported by different and nonoverlapping author groups, in different sites and different years, with nonoverlapping subject groups. Thus, it is difficult to see how their independence can be doubted. The six studies were not, of course, randomly selected (they were the entire known population of such studies); random selection is appropriate only when the entire population is too large to conveniently study. Their third objection is of course valid: if one of the six studies had favored the 3-dB rather than the 5-dB ER, the sign test would not have been statistically significant. That
University of Texas Health Science Center, San Antonio, Texas, USA; and 2Program in Audiology and Communication Sciences, Washington University School of Medicine, St. Louis, Missouri, USA.
1
0196/0202/2015/364-0492/0 • Ear & Hearing • Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved • Printed in the U.S.A. 492
LETTER TO THE EDITOR
is why we characterized this result as only suggestive of a nonrandom outcome. NIOSH questions the “suitability” of re-examining the human NIPTS data, “excluding robust animal studies and temporary threshold shift [TTS] studies” that also address the ER issue. We clearly indicated in our article that all three of these study types can shed light on the ER issue and should be of interest to regulatory agencies. We also cited reviews of animal permanent threshold shift and human TTS data that would support the 3-dB ER only for brief uninterrupted exposures. NIOSH now considers the available human NIPTS data to be based on “outdated methodologies” (presumably the lack of modern dosimetry); but NIOSH (1998) considered these data not only worthy of discussion but also supportive of their recommendation of a 3-dB ER. To arrive at that conclusion, both NIOSH and Suter (1992) relied heavily on Passchier-Vermeer’s (1973) nonpeer-reviewed synthesis of 11 studies of human NIPTS, with no mention of most of the individual studies. Our approach was to review each of these 11 papers and other relevant studies; this was no small task because several of the studies required translation before we could read them. We concluded that the human NIPTS data do not support the 3-dB ER. NIOSH assumes that sound level measurements made before about 1980 would have overpredicted hearing loss (in other words, sound level readings would have been too high). However, neither of their cited references (two abstracts by Earshen 1980, 1994) suggests systematic overestimation of exposure by earlier sound level measurements. We clearly indicated in our paper that hazard estimates for exposures rich in impact or impulse noise might require additional considerations, such as the measurement of kurtosis. Although we disagree with NIOSH’s assertion that these alternative metrics have been demonstrated to be more accurate, that discussion is outside the scope of our article. Incidentally, one of the articles they cite regarding kurtosis (Lataye & Campo 1996) does not mention kurtosis and shows (in chinchillas) that the 5-dB ER predicted NIPTS better than the 3-dB ER for most of their noise exposures. The NIOSH and Suter letters rely extensively on endorsements from professional and governmental organizations, implying that if enough such organizations support the 3-dB ER, the subject is closed. We hope that most readers agree with us that nothing in science can ever be immune to criticism and re-examination. We have read the position statements of most of the organizations they mention and find that with few if any exceptions, they have not reviewed primary literature other than the sources that we included in our article. Most of them rely directly or indirectly—as did Suter and NIOSH—on PasschierVermeer (1973), a synthesis that we believe to be unreliable. Others may support the 3-dB ER for a more defensible reason: a wish to be overprotective in regulation (many employers require everyone in areas where average levels exceed 85 dBA to wear HPDs; this rule, equivalent to a zero-dB ER, is clearly overprotective for people passing through briefly but might be justified on the basis of simplicity and enforceability). As we acknowledged, the 5-dB ER could be more accurate for most exposures but still might underpredict hazard for some exposures, such as brief uninterrupted exposures. In addition to Suter (1992) and NIOSH (1998), NIOSH cites four other papers that they claim addressed “the rationale for using the 3-dB exchange rate,” but none of these four reports
493
provides any new information that would support that ER. Prince et al (1997) used only the 5-dB ER to predict the hearing levels in their subjects, never suggested that it was inadequate, and never mentioned any other ER. Stephenson et al (2010) wrote a letter to the editor that simply cited other reviews and position statements. Murphy and Kardous (2012) was a NIOSH report limited to impulse and impact noise metrics, which is outside the scope of our article. Themann et al. (2013) was a NIOSH review that neither presented nor cited data supporting any ER. NIOSH objects to our focus on people with intermittent or fluctuating exposures as a “subgroup of workers who are least exposed to hazardous noise.” We found this surprising. First, hazard obviously depends on both noise level and duration. High-level intermittent noise can be more hazardous than continuous low-level noise. Second, assessing hazard for intermittent/fluctuating exposures is the main point of choosing an ER. For truly continuous 8-hr noise exposures, the ER does not matter! NIOSH claims that there is “overwhelming evidence that many workers in programs using this exchange rate [5-dB] are sustaining noise-induced hearing loss [NIHL]” and supports this by reference to “staggering information” from the Bureau of Labor Statistics (2013). The cited data show that about 11 of every 10,000 manufacturing workers had standard threshold shifts (STSs) recorded in 2012 (rates were much lower for all other industry sectors). There are many causes for STSs in HCPs, including age-related threshold shifts, audiometric testretest variability, headphone reversals during testing, and ear diseases, in addition to NIHL, which can be caused by occupational and/or nonoccupational exposures. STS cases caused by occupational noise can in turn be attributable to many factors, including employer failure to enforce regulations and employee failure to comply with the use of HPDs. NIOSH implies that the inadequacy of current OSHA regulations, including the use of the 5-dB ER, is the cause of these threshold shifts and states, “a more conservative exchange rate has the best potential to reduce noise exposures and the burden of noise-induced hearing loss.” We know of no evidence for these two positions, and NIOSH cites none. It is unclear to us how a change in the ER would motivate employers to implement better HCPs and to put more emphasis on noise control, or how including more workers in those programs would motivate workers to more faithfully use HPDs Seixas et al. (2005a, cited by Suter) compared different noise exposure metrics to each other but contained no hearing threshold data, did not evaluate the accuracy of these metrics in predicting noise-induced shifts, and thus appears to be irrelevant to the point being made in Suter’s letter. Perhaps Suter meant to cite Seixas et al. (2005b), which showed that after 3 years, construction apprentices had experienced changes in 4 kHz thresholds that were “extremely small, and not significantly different from zero.” Seixas et al. noted that the longitudinal shifts were less than predicted by the ISO-1999 model, using the 3-dB ER and that the intermittency of construction exposure was among the possible explanations for this discrepancy. They acknowledged that findings like this supported the 5-dB ER but suggested that other explanations were more plausible. Seixas et al. (2012) presented the 10-year longitudinal data for the same apprentice group and cautiously asserted that the “relatively small” mean threshold shifts at 4 kHz (2 to 3 dB per 10 dBA
494
LETTER TO THE EDITOR
exposure level increase) were “somewhat higher” than and “consistent with or exceeded” those predicted by the ISO-1999 model. Their analysis had two flaws that render this conclusion even more tenuous than they stated. First, the ISO model predicts median, not mean shifts; hearing threshold distributions are almost always positively skewed, such that means are higher than medians. Second, Seixas et al. assumed that the 12-dB mean threshold at baseline was entirely attributable to noise exposure before the onset of the study, and then used the model to generate an estimate of only 1 dB of additional shift for the next 10 years. Median 4 kHz threshold for U.S. men at age 30 yr is 7 dB (per Hoffman et al. 2010), and the mean would be higher; this might support an estimate of prior NIPTS of 5 dB or less (12 minus 7). With that assumption, the ISO model predicts that 10 yr of additional exposure at 87 dBA will yield an additional 3 dB or more of NIPTS (median, not mean). With these points taken into consideration, the threshold shifts experienced by these apprentices were either consistent with or less than those predicted by ISO-1999. We disagree with Suter’s interpretation of the data reported by Davis et al. (2012). These authors compared hearing thresholds predicted by ISO-1999 (based on a subject’s age, sex, and noise exposure) to their actual thresholds. Unfortunately, they made two important errors that biased their results. First, Davis et al. compared subjects’ binaural average thresholds to the better-ear thresholds in Annex B of ISO-1999 (1990). The underlying data in Annex B (Glorig & Roberts 1965) show that binaural average thresholds were 4 to 5 dB higher than better-ear thresholds, for the frequencies and age groups represented in Davis et al. (2012). Second, it appears that Davis et al. presented subject group median thresholds without making the 2.5-dB correction that is necessary before comparison with these Annex B medians, assuming that the medians had been calculated in the conventional way (Hoffman et al. 2010). In combination, these errors would make the differences between their subjects’ hearing and ISO-1999 predictions seem about 7 dB worse than they really were. Figure 2 in Davis et al. (2012) summarizes data for all their subjects; median thresholds appeared to be 1 to 8 dB worse than predicted. With appropriate corrections as indicated earlier, these differences would disappear. Suter states that ISO-1999 (1990) is based on data from Passchier-Vermeer (1973), as well as those of Baughn (1973); that is incorrect. The Passchier-Vermeer data that went into the development of ISO-1999 (1990) were not the intermittent/fluctuating noise data that were reviewed by us (Passchier-Vermeer 1973), but her data on people exposed to steady state noise (PasschierVermeer 1968). Neither the Baughn data nor the Passchier-Vermeer (1973) data were included in the ISO-1999 (1990) model, as explained by Johnson (1978, 1988), who created the model. Suter suggests that pure-tone thresholds may be an inadequate measure of NIHL, citing a study of cochlear nerve degeneration after TTS in mice (Kujawa & Liberman 2009). She also cites a finding of progressive hearing loss after a single noise exposure in adolescent mice (Kujawa & Liberman 2006). If these phenomena occur in humans, it seems unlikely that they would occur with exposures below the current OSHA exposure limits (and therefore the stricter exposure limits recommended by NIOSH would have no effect, at least with respect to these hypothetical problems in humans). The mouse exposures caused very large and persistent TTS (>40 dB, 24 hr later); TTS of that magnitude in humans would require an exposure well above the OSHA permissible limit.
The longitudinal studies that Suter cites to support the hypothesis of progressive noise-induced damage after the cessation of noise lack data on noise exposure (Gates et al. 2000) and statistical analysis (Rosenhall 2003). Many studies that include both noise exposure data and statistical analysis do not support this hypothesis (Rösler 1994; Lee et al. 2005; Cruickshanks et al. 2010; Albera et al. 2010; Hoffman 2015). Suter states that our comment that the essence of public policy decisions is balancing costs and benefits is a “misrepresentation of public policy.” We disagree. Her statement is based on a narrow reading of the language of the OSHA enabling legislation but does not consider almost 30 years of presidential executive orders. In 1982, President Reagan issued an executive order requiring agencies to use cost-benefit analysis (Exec. Order No. 12,291, 3 C.F.R. 127, 1982). Thus, in the final Hearing Conservation Amendment published in 1983, OSHA no longer claimed exemption from considering both costs and benefits. In 1994 President Clinton issued an order on the same topic, requiring agencies to include qualitative measures of costs and benefits (Exec. Order No. 12,866, 3 C.F.R. 638, 639, 1994). In 2011, President Obama issued Executive Order 13,563 requiring all federal regulations to “take into account benefits and costs, both quantitative and qualitative.” Our statement regarding costs and benefits was consistent with executive orders spanning three decades. Neither Suter nor NIOSH offered any alternative analysis of the 10 studies we excluded from our summary table, or of the nine studies we included in that table, that would support the 3-dB ER. Furthermore, neither Suter nor NIOSH presented any additional data supportive of the 3-dB ER (e.g., evidence that workers whose employers’ HCPs use the 3-dB ER experience less hearing loss than workers whose employers’ HCPs use the 5-dB ER). Their main position now appears to be that the human NIPTS data are unreliable and cannot be used to question the 3-dB ER (logically, that would mean that these data cannot be used to support the 3-dB ER, either). Our article recommended prospective longitudinal research that could provide better NIPTS data to address the ER, and NIOSH now agrees. As a federal agency with an annual research budget (2014) over $100 million, NIOSH could have funded studies on this type anytime in the 20 years since they began to advocate for the 3-dB ER (NIOSH 1995). We urge them to do so now. To summarize, we appreciate the interest of Suter and NIOSH in our article, but find their arguments unpersuasive. Many of their assertions are incorrect, and others are irrelevant, as described earlier. Although we disagree with many of their positions, we value the opportunity to participate in a full discussion of the many important issues in this area.
REFERENCES Albera, R., Lacilla, M., Piumetto, E., et al. (2010). Noise-induced hearing loss evolution: Influence of age and exposure to noise. Eur Arch Otorhinolaryngol, 267, 665–671. Baughn, W. L. (1973). Relation Between Daily Noise Exposure and Hearing Loss as Based on the Evaluation of 6835 Industrial Noise Exposure Cases. AMRL-TR-73 (AD 767 204). Wright-Patterson Air Force Base, OH: Aerospace Medical Research Laboratory. Bureau of Labor Statistics. (2013). Employer-Reported Workplace Injuries and Illnesses–2012. Washington, DC: Bureau of Labor Statistics, United States Department of Labor. Retrieved November 21, 2014, from http:// www.bls.gov/news.release/pdf/osh.pdf.
LETTER TO THE EDITOR
Cruickshanks, K. J., Nondahl, D. M., Tweed, T. S., et al. (2010). Education, occupation, noise exposure history and the 10-yr cumulative incidence of hearing impairment in older adults. Hear Res, 264, 3–9. Davis, R. I., Qiu, W., Heyer, N. J., et al. (2012). The use of the kurtosis metric in the evaluation of occupational hearing loss in workers in China: Implications for hearing risk assessment. Noise Health, 14, 330–342. Earshen, J. J. (1980). Noise dosimeters: On measurement reliability and instrument accuracy. J Acoust Soc Am, 68, S21–S21. Earshen, J. J. (1994). On comparing noise metrics applied to hearing conservation. J Acoust Soc Am, 96, 3272. Gates, G., Schmid, P., Kujawa, S., et al. (2000). Longitudinal threshold changes in older men with audiometric notches. Hearing Res, 141, 220–228. Glorig, A., & Roberts, J. (1965). National Center for Health Statistics: Hearing Levels of Adults by Age and Sex United States 1960–1962. Vital and Health Statistics, PHS Publication Number 1000 Series 11, No. 11. Washington, DC: Public Health Service, US Government Printing Office. Hoffman, H. J. (2015). Age-related hearing loss: Predicted age-specific incidences based on cross-sectional prevalences, compared with observed age-specific incidences from a longitudinal study. ARO Abstracts, 38, 190. Hoffman, H. J., Dobie, R. A., Ko, C. W., et al. (2010). Americans hear as well or better today compared with 40 years ago: Hearing threshold levels in the unscreened adult population of the United States, 1959-1962 and 1999-2004. Ear Hear, 31, 725–734. Holmgren, G., Johnsson, L., Kylin, B., et al. (1971). Noise and hearing of a population of forest workers. Br Ac Soc Spec, 1, 35–42. International Organization for Standardization. (1990). Acoustics: Determination of Occupational Noise Exposure and Estimation of Noise-Induced Hearing Impairment, ISO-1999. Geneva: International Organization for Standardization. Johansson, B., Kylin, B., Reopstorff, S. (1973). Evaluation of the hearing damage risk from intermittent noise according to the ISO recommendations. Proceedings of the International Congress on Noise as a Public Health Problem. EPA Report 550/9-73-008. Johnson, D. L. (1978). Derivation of Presbyacusis and Noise-Induced Permanent Threshold Shift (NIPTS) to Be Used for the Basis of a Standard on the Effects of Noise on Hearing. AMRL-TR-78-128. Wright-Patterson Air Force Base, OH: Armstrong Medical Research Laboratory. Johnson, D. L. (1988). Risk of hearing loss from noise. Semin Hear, 9, 279–284. Kujawa, S. G., & Liberman, M. C. (2006). Acceleration of age-related hearing loss by early noise exposure: Evidence of a misspent youth. J Neurosci, 26, 2115–2123. Kujawa, S. G., & Liberman, M. C. (2009). Adding insult to injury: Cochlear nerve degeneration after “temporary” noise-induced hearing loss. J Neurosci, 29, 14077–14085. Lataye, R., & Campo, P. (1996). Applicability of the L(eq) as a damage-risk criterion: An animal experiment. J Acoust Soc Am, 99, 1621–1632. Lee, F. S., Matthews, L. J., Dubno, J. R., et al. (2005). Longitudinal study of pure-tone thresholds in older persons. Ear Hear, 26, 1–11. Martin, R. H., Gibson, E. S., Lockington, J. N. (1975). Occupational hearing loss between 85 and 90 dBA. J Occup Med, 17, 13–18. Murphy, W. J., & Kardous, C. A. (2012). In-Depth Survey Report: A Case for Using A-Weighted Equivalent Energy as a Damage-Risk Criterion. Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, EPHB-350-11a. NIOSH. (1972). NIOSH Criteria for a Recommended Standard: Occupational Exposure to Noise. Cincinnati, OH: U.S. Department of Health, Education, and Welfare, Health Services and Mental Health
495
Administration, National Institute for Occupational Safety and Health, DHEW (NIOSH). Publication No. HSM 73-11001. NIOSH. (1976). Survey of Hearing Loss in the Coal Mining Industry. Cincinnati, OH: U.S. Department of Health, Education, and Welfare, Public Health Service, Center for Disease Control, National Institute for Occupational Safety and Health (NIOSH) Publication No. 76-172. NIOSH. (1982). Health Hazard Evaluation Report. Newburgh Fire Department, Newburgh, NY. Cincinnati OH: U.S. Department of Health and Human Services, Public Health Service, Center for Disease Control, National Institute for Occupational Safety and Health (NIOSH) Publication No. HETA 81–059–1045. NIOSH. (1995). Health Hazard Evaluation Report 95-0167-2539. The Western States Machine Company, Hamilton, Ohio. Cincinnati OH: U.S. Department of Health and Human Services, Public Health Service, Center for Disease Control, National Institute for Occupational Safety and Health, DHEW (NIOSH) Publication No. HETA 95-0167-2539. NIOSH. (1998). NIOSH Criteria for a Recommended Standard: Occupational Noise Exposure Revised Criteria 1998. Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control, National Institute for Occupational Safety and Health, DHHS. Publication No. 98–126. OSHA. (1983). Department of Labor Occupational Noise Exposure Standard. US Department of Labor, Occupational Safety and Health Administration, CFR29 (XVII) 1910.95. Passchier-Vermeer W. (1968). Hearing loss due to exposure to steady-state broadband noise. Report # 35, Institute for Public Health Eng. (sound and light division), The Netherlands. Passchier-Vermeer, W. (1973). Noise-induced hearing loss from exposure to intermittent and varying noise. In Proceedings of the International Congress on Noise as a Public Health Problem. EPA Report 550/9-73-008. Prince, M. M., Stayner, L. T., Smith, R. J., et al. (1997). A re-examination of risk estimates from the NIOSH Occupational Noise and Hearing Survey (ONHS). J Acoust Soc Am, 101, 950–963. Rosenhall, U. (2003). The influence of ageing on noise-induced hearing loss. Noise Health, 5, 47–53. Rösler, G. (1994). Progression of hearing loss caused by occupational noise. Scand Audiol, 23, 13–37. Sataloff, J., Vassallo, L., Menduke, H. (1969). Hearing loss from exposure to interrupted noise. Arch Environ Health, 18, 972–981. Seixas, N., Neitzel, R., Sheppard, L., et al. (2005a). Alternative metrics for noise exposure among construction workers. Ann Occup Hyg, 49, 493–502. Seixas, N. S., Goldman, B., Sheppard, L., et al. (2005b). Prospective noise induced changes to hearing among construction industry apprentices. Occup Environ Med, 62, 309–317. Seixas, N. S., Neitzel, R., Stover, B., et al. (2012). 10-Year prospective study of noise exposure and hearing damage among construction workers. Occup Environ Med, 69, 643–650. Stephenson, M. R., Byrne, D. C., Ohlin, D. W., et al. (2010). Perspectives on “Efficacy of the U.S. Army policy on hearing conservation programs.” Mil Med, 175, xii–xvi. Suter, A. H. (1992). The relationship of the exchange rate to noise-induced hearing loss. Report for the Doc. Development Branch, Div. of Standards Development and Technology Transfer, NIOSH, Public Health Service, U.S. Dept. of Health and Human Services. Themann, C., Suter, A. H., Stephenson, M. R. (2013). National Research Agenda for the Prevention of Occupational Hearing Loss—Part 1. Semin Hear, 34, 145–207. Thierry, L., Damongeot, A., Derzko, G., et al. (1978). Etude des risques auditifs auxquels sont soumis les salaries argricoles en exploitations forestieres et en scieries. Report for the Institut National de Recherche et de Securite (INRS), Vandoeuvere-Les-Nancy, France.
