9
Readers' forum
Daniel Paludo Brunetto Leonardo Koerich M^onica Tirre de Souza Ara ujo Rio de Janeiro, Brazil Am J Orthod Dentofacial Orthop 2015;147:8-9 0889-5406/$36.00 Copyright Ó 2015 by the American Association of Orthodontists. http://dx.doi.org/10.1016/j.ajodo.2014.10.017
REFERENCES 1. Al-Kabab F, Ghoname N, Banabilh S. Proposed regression equations for prediction of the size of unerupted permanent canines and premolars in Yemeni sample. J Orthod Sci 2014;3:68-73. 2. Palmer PB, O'Connell DG. Regression analysis for prediction: understanding the process. Cardiopulm Phys Ther J 2009;20:23-6. 3. Pedhazur E. Multiple regression in behavioral research. Fort Worth, Tex: Harcourt Brace College Publishers; 1997.
Treatment effectiveness of the Fr€ankel function regulator on Class III malocclusion
W
e read with great interest the systematic review of the Fr€ankel appliance in the August 2014 issue of the Journal (Yang X, Li C, Bai D, Su N, Chen T, Xu Y, et al. Treatment effectiveness of Fr€ankel function regulator on the Class III malocclusion: A systematic review and meta-analysis. Am J Orthod Dentofacial Orthop 2014;146:143-54). This review challenged the common presumption that the longused Fr€ankel function regulator was effective in managing Class III malocclusions. However, we believe that there was a mistake in the inclusion of the trials. We noticed that the number of participants in a trial conducted by Waheed-Ul-Hameed1 was too small (only 10 in each group). Having too few participants would certainly increase the probability of type II error (risk of false-negative). It seemed that there lacked sample-size estimation in the trial conducted by Waheed-Ul-Hameed. Yet the authors assessed this trial as “high quality” in the Newcastle-Ottawa scale and included it in the meta-analysis. As a result, except for the comparison of “overjet changes,” which could not serve as the primary outcome, there was a wide confidence interval in every other pooled analysis. The lack of statistical accuracy of this trial due to limited participants would influence the overall pooled result. Thus, this trial should not be included in the meta-analysis, or subgroup analysis is needed excluding the trial. Also, the scale assessment should be modified.
Bo-Xi Yan Xue-Dong Wang Yan-Heng Zhou Beijing, China Am J Orthod Dentofacial Orthop 2015;147:9 0889-5406/$36.00 Copyright Ó 2015 by the American Association of Orthodontists. http://dx.doi.org/10.1016/j.ajodo.2014.10.014 REFERENCE 1. Waheed-Ul-Hameed M. Cephalometric evaluation of maxillary retrognathism cases treated with FR-3 appliance. PODJ 2002;22: 25-30.
Authors' response
W
e thank Drs Yan, Wang, and Zhou for their interest in our study (Yang X, Li C, Bai D, Su N, Chen T, Xu Y, Xianglong H. Treatment effectiveness of Fr€ankel function regulator on the Class III malocclusion: A systematic review and meta-analysis. Am J Orthod Dentofacial Orthop 2014;146:143-54). They thought that there was a mistake about including a trial with a small sample conducted by Waheed-Ul-Hameed,1 but we must point out that it was not. First, the purpose of a meta-analysis is to increase the power of detecting a real effect as statistically significant by combining several small samples.2 If a trial was excluded because of its small sample size, how could a meta-analysis be made? In addition, the inclusion process was conducted according to previous protocol, which was based on the instructions in the Cochrane Handbook, and the sample size was not in the inclusion criteria. Second, the authors considered that the trial should not be assessed as “high quality” because of the small sample size. Actually, we had already presented the items and criteria for quality assessment with the Newcastle-Ottawa scale for cohort studies in Table I, and sample size was not included in the quality assessment system.3 Third, the authors said that too few participants would certainly cause the probability of type II error (risk of false-negative) increasing. However, too few participants could cause not only type II error but also type I error (risk of false-positive). Definitely, the chance of type I and type II errors cannot be avoided but can be controlled by regulating the value of a and b statistically, and the increase of causing type II error would decrease the probability of type I error.4 Most importantly, what we have done was a systematic review of interventions, but not diagnostic accuracy; therefore, the
American Journal of Orthodontics and Dentofacial Orthopedics
January 2015 Vol 147 Issue 1
Readers' forum
Daniel Paludo Brunetto Leonardo Koerich M^onica Tirre de Souza Ara ujo Rio de Janeiro, Brazil Am J Orthod Dentofacial Orthop 2015;147:8-9 0889-5406/$36.00 Copyright Ó 2015 by the American Association of Orthodontists. http://dx.doi.org/10.1016/j.ajodo.2014.10.017
REFERENCES 1. Al-Kabab F, Ghoname N, Banabilh S. Proposed regression equations for prediction of the size of unerupted permanent canines and premolars in Yemeni sample. J Orthod Sci 2014;3:68-73. 2. Palmer PB, O'Connell DG. Regression analysis for prediction: understanding the process. Cardiopulm Phys Ther J 2009;20:23-6. 3. Pedhazur E. Multiple regression in behavioral research. Fort Worth, Tex: Harcourt Brace College Publishers; 1997.
Treatment effectiveness of the Fr€ankel function regulator on Class III malocclusion
W
e read with great interest the systematic review of the Fr€ankel appliance in the August 2014 issue of the Journal (Yang X, Li C, Bai D, Su N, Chen T, Xu Y, et al. Treatment effectiveness of Fr€ankel function regulator on the Class III malocclusion: A systematic review and meta-analysis. Am J Orthod Dentofacial Orthop 2014;146:143-54). This review challenged the common presumption that the longused Fr€ankel function regulator was effective in managing Class III malocclusions. However, we believe that there was a mistake in the inclusion of the trials. We noticed that the number of participants in a trial conducted by Waheed-Ul-Hameed1 was too small (only 10 in each group). Having too few participants would certainly increase the probability of type II error (risk of false-negative). It seemed that there lacked sample-size estimation in the trial conducted by Waheed-Ul-Hameed. Yet the authors assessed this trial as “high quality” in the Newcastle-Ottawa scale and included it in the meta-analysis. As a result, except for the comparison of “overjet changes,” which could not serve as the primary outcome, there was a wide confidence interval in every other pooled analysis. The lack of statistical accuracy of this trial due to limited participants would influence the overall pooled result. Thus, this trial should not be included in the meta-analysis, or subgroup analysis is needed excluding the trial. Also, the scale assessment should be modified.
Bo-Xi Yan Xue-Dong Wang Yan-Heng Zhou Beijing, China Am J Orthod Dentofacial Orthop 2015;147:9 0889-5406/$36.00 Copyright Ó 2015 by the American Association of Orthodontists. http://dx.doi.org/10.1016/j.ajodo.2014.10.014 REFERENCE 1. Waheed-Ul-Hameed M. Cephalometric evaluation of maxillary retrognathism cases treated with FR-3 appliance. PODJ 2002;22: 25-30.
Authors' response
W
e thank Drs Yan, Wang, and Zhou for their interest in our study (Yang X, Li C, Bai D, Su N, Chen T, Xu Y, Xianglong H. Treatment effectiveness of Fr€ankel function regulator on the Class III malocclusion: A systematic review and meta-analysis. Am J Orthod Dentofacial Orthop 2014;146:143-54). They thought that there was a mistake about including a trial with a small sample conducted by Waheed-Ul-Hameed,1 but we must point out that it was not. First, the purpose of a meta-analysis is to increase the power of detecting a real effect as statistically significant by combining several small samples.2 If a trial was excluded because of its small sample size, how could a meta-analysis be made? In addition, the inclusion process was conducted according to previous protocol, which was based on the instructions in the Cochrane Handbook, and the sample size was not in the inclusion criteria. Second, the authors considered that the trial should not be assessed as “high quality” because of the small sample size. Actually, we had already presented the items and criteria for quality assessment with the Newcastle-Ottawa scale for cohort studies in Table I, and sample size was not included in the quality assessment system.3 Third, the authors said that too few participants would certainly cause the probability of type II error (risk of false-negative) increasing. However, too few participants could cause not only type II error but also type I error (risk of false-positive). Definitely, the chance of type I and type II errors cannot be avoided but can be controlled by regulating the value of a and b statistically, and the increase of causing type II error would decrease the probability of type I error.4 Most importantly, what we have done was a systematic review of interventions, but not diagnostic accuracy; therefore, the
American Journal of Orthodontics and Dentofacial Orthopedics
January 2015 Vol 147 Issue 1
