ORIGINAL ARTICLE
Preferred Presentation of the Visual Analog Scale for Measurement of Postoperative Pain Helle Birgitte Kjeldsen, RN*; Tobias Wirenfeldt Klausen, MS†; Jacob Rosenberg, DSc* *Department of Surgery, Herlev Hospital, Herlev; †Department of Hematology, Herlev Hospital, Herlev, Denmark
& Abstract Background: The aim of this study was to evaluate differences in pain scores with different visual analog scale (VAS) presentations and to compare those differences with a numeric rating scale. We also asked the patients for preference of the different methods. Methods: Prior to the trial, we performed power calculations to estimate a preferred sample size, and 62 postoperative patients supplied a complete set of data to the study. Inclusion criteria were newly operated patients within the first 5 days after surgery. Every patient included was with 1minute intervals and presented with one of the following 100-mm VAS lines: VAS horizontal with or without stop lines at the endings, or VAS vertical with or without stop lines. They also completed a numeric rating scale (NRS). Results: We did not find differences in pain scores between the four VAS measures. The NRS had slightly higher pain scores than VAS, especially at low levels of pain. Patients preferred the NRS as compared to the VAS, and when choosing between the four different VAS presentations, they preferred the horizontal VAS with stop lines at the ends. Conclusion: For daily clinical practice for guiding postoperative analgesic treatment, the NRS seems to be a good option measuring pain reliably with good patient understanding
Address correspondence and reprint requests to: Jacob Rosenberg, DSc, Department of Surgery, Herlev Hospital, Herlev Ringvej 75 Herlev 2730, Denmark. E-mail: [email protected]. Funding: The study did not receive any funding. Conflict of interest: The authors have no conflict of interest. Submitted: April 6, 2015; Revision accepted: June 17, 2015 DOI. 10.1111/papr.12344
© 2015 World Institute of Pain, 1530-7085/15/$15.00 Pain Practice, Volume , Issue , 2015 –
and acceptance. For pain research, where there may be more time to explain the method and when a scale with more data points may be preferred, a VAS horizontal including stop lines at the ends can be recommended. & Key Words: pain, postoperative, visual analog scale, numeric rating scale, patient preference
INTRODUCTION The visual analog scale (VAS) has been used for measuring both acute and chronic pain since 1966.1,2 Measurement of unpleasant, subjective phenomena such as nausea, fatigue, dyspnea, and pain are experiences that require self-report.3 VAS is a simple and often used paingrading tool to measure such subjective symptoms.1,3 Commonly, a VAS is formed as a 100-mm horizontal line, and in this form, it has been shown to produce a more uniform distribution of pain scores than a vertical VAS.1 Patients are instructed to grade the pain intensity by marking a 100-mm line anchored with terms describing the extremes of the intensity of pain.4 Studies have found that the pain scores from the horizontal scale tended to be slightly lower than that from the vertical scale.5 Therefore, the application of VAS is ambiguous, as it has been shown that different methods of applying VAS are being used: VAS vertical, with and without endpoints; VAS horizontal, with and without endpoints; and to a further extent, up to 24 different adjectives have been used describing the extremes at the VAS lines. Commonly, the adjectives chosen are in some form of “no pain” and “worst imaginable pain”.2,4
2
KJELDSEN ET AL.
The aim of the study was to evaluate whether patients would grade themselves differently, depending on which VAS presentation/form was used and which presentation the patients preferred.
METHODS All patients 1 to 5 days after operation in the departments of surgery, gynecology, and orthopedic surgery, and those fulfilling the inclusion criteria were screened for candidacy during March 2014. Inclusion criteria were newly operated patients within the first 5 days after surgery, informed consent, and age > 18 years. Exclusion criteria were prior participants, linguistic challenges, or whether the patients were physically or mentally unstable to an extent that they could not understand the research question. Every patient included was with 1-minute intervals and presented with one of the following 100-mm VAS lines: VAS horizontal with or without stop lines at the endings, or VAS vertical with or without stop lines (Figure 1). With one stroke across the VAS line, the patient was asked to indicate the level of pain currently perceived in a state of rest. When the patient had indicated the current pain sensation on all four VAS lines, the patient was also asked to give a numerical representation of the pain sensation, on a scale ranging from 1 to 10 (corresponding to NRS) in a state of rest. Finally, the interviewer would ask the patient what the preferred method of pain grading had been. To this, the patient was presented with three scenarios: VAS horizontal vs. VAS vertical, VAS with endpoints vs. VAS without endpoints, and VAS vs. NRS. To each answer, the patient was allowed to answer one of the two or “indifferent”. The patient was asked to provide a
Worst pain imaginable
No pain
Worst pain imaginable
No pain
Worst pain imaginable
No pain
comment for the choices he/she had made. The orders of the four VAS lines were randomized using a randomization generator (www.randomization.com). The randomization generator created a random permutation of the four VAS lines, to assure that all candidates received the four VAS lines in random order (Figure 1). The study was approved by the Danish Data Protection Agency (HEH-2014-054) and was posted on www.clinicaltrials.gov (NCT02243410). The study was exempted for approval by the local ethics committee because it was regarded as a quality assurance study without biomedical interventions (H-4-2014-fsp). All patients participated after providing an informed consent. Prior to the trial, we performed power calculations to estimate a preferred sample size. From an expected intraclass correlation (ICC) of 0.8, it would require a sample size of 61, to gain an 80% certainty of having a lower boundary of 95% and a confidence interval above 0.65. In total, 62 postoperative patients supplied a complete set of data to the study. Agreement between different VAS scores and NRS score was inspected using ICC and Bland–Altman plots. Differences in values between scores were analyzed using paired t-test or repeated-measures ANOVA. Patient preferences were analyzed using frequencies, and significance were analyzed by comparison of preference in one direction vs. the other direction using a binomial test with a 50% reference ignoring neutral answers. All tests were two sided. P < 0.05 was regarded as statistically significant, and limits of confidence were 95%. All statistics was performed using SPSS version 19.0 (IBM corp., Armonk, NY, U.S.A.) or R version 3.1.0 (R Foundation for Statistical Computing, Vienna, Austria).
Worst pain imaginable
No pain
Figure 1. All four visual analog scale (VAS) lines used in the research were 10 cm in actual length.
Patient Pain Measurement Preference 3
RESULTS Two patients had major internal disagreements that indicated a general misconception of the VAS lines. We excluded these patients from the analyses except for the analyses of patient preferences. A sensitivity analysis was performed to inspect whether the inclusion of these patients would generate different conclusions. We did not find different results including these patients. High levels of agreement were found between all five measures. Intraclass correlation coefficients were in the range of 0.93 to 0.98, and all comparisons had lower limits of confidence intervals above 0.8. NRS had equal agreement between the VAS scores as VAS scores had between each other, and we did not find any pattern in the values. Results are shown in Table 1. We did not find differences in mean scores between the four VAS measures (P = 0.5). The NRS had significantly higher mean scores than all VAS scores. Mean differences were 0.42 (95% CI: 0.19; 0.66, P = 0.0007), 0.51 (95% CI: 0.27; 0.74, P < 0.0001), 0.37 (95% CI: 0.14; 0.60, P = 0.002), and 0.36 (95% CI: 0.11; 0.62, P = 0.006). Results are shown in Table 2. In a Bland– Altman plot (Figure 2) comparing the difference between NRS and VAS (horizontal and including end lines), we saw a tendency toward higher NRS scores when patients had low mean pain scores, whereas the scores seemed similar when patients had high mean
scores. Patients with a mean score below 5 had a mean difference at 0.64 and those with a mean score above 5 had a mean difference at 0.31 (P = 0.0004). Of 62 patients, 22 patients (35%) had a preference toward VAS horizontal compared to VAS vertical 9 (15%) (P = 0.04). Thirty-two patients (52%) were neutral. Results are shown in Table 3. As a further notion, 22 (35%) patients voiced that it was easier to understand VAS with endpoint compared to 4 (6%) patients preferring VAS without endpoints (P = 0.0005), though 36 (58%) patients were neutral. Of the 62 participants, 32 (52%) had NRS as the preferred means and 15 (24%) had VAS as their preferred (P = 0.02), with 15 (24%) patients being neutral.
DISCUSSION We found that the different VAS scores were similar, but the NRS had slightly higher scores than all VAS scores, mainly if pain levels were low. Patient preference pointed at the horizontal VAS with endpoints or the NRS for the measurement of postoperative pain. Multiple studies have described the differences found between the existing pain-grading tools, which are most commonly used among clinicians and researchers.6–8 These entail the visual analog scale (VAS), numerical rating scale (NRS), verbal rating scale (VRS), and faces
Table 1. Intraclass Correlation Coefficients (ICC) Between the Five Measures
VAS VAS VAS VAS NRS
horizontal with endpoints horizontal without endpoints vertical with endpoints vertical without endpoints
VAS Horizontal with Endpoints
VAS Horizontal Without Endpoints
VAS Vertical with Endpoints
VAS Vertical Without Endpoints
– 0.97 0.97 0.93 0.94
– 0.98 (0.97; 0.99) 0.96 (0.93; 0.98) 0.94 (0.85; 0.97)
– 0.97 (0.95; 0.98) 0.95 (0.90; 0.97)
– 0.94 (0.88; 0.96)
(0.95; (0.95; (0.89; (0.88;
0.98) 0.98) 0.96) 0.97)
Table shows ICC, including 95% confidence limits. VAS, visual analog scale; NRS, numeric rating scale.
Table 2. Comparisons Between Mean Scores VAS Comparison
VAS VAS VAS VAS NRS
horizontal with endpoints horizontal without endpoints vertical with endpoints vertical without endpoints
Mean (SD)
Mean Difference (95% CI)
3.05 2.96 3.10 3.11 3.47
Reference value 0.08 ( 0.27; 0.10) 0.05 ( 0.15; 0.25) 0.06 (0.22; 0.34) –
(2.98) (2.86) (3.04) (2.99) (2.79)
Overall P for VAS comparison: P = 0.5; overall P for NRS-VAS comparison: P < 0.0001. VAS, visual analog scale; NRS, numeric rating scale.
NRS-VAS Comparison P – 0.4 0.6 0.7 –
Mean Difference (95% CI) 0.42 ( 0.66; 0.19) 0.51 ( 0.74; 0.27) 0.37 ( 0.60; 0.14) 0.36 ( 0.62; 0.11) Reference value
P 0.0007 < 0.0001 0.002 0.006 –
4
KJELDSEN ET AL.
Figure 2. Bland–Altman plot of the difference between numeric rating scale (NRS) and visual analog scale (VAS) plotted against the mean of NRS and VAS. The three lines represent average difference (solid line) and 95% limits of agreement (1.96 SD).
Table 3. Patient Preferences N (%) VAS horizontal vs. vertical Horizontal preferred Vertical preferred Neutral or no opinion P Endpoints Endpoints preferred No endpoints preferred Neutral or no opinion P VAS vs. NRS VAS preferred NRS preferred Neutral or no opinion* P
21 (34) 9 (15) 32 (52) 0.04 22 (35) 4 (6) 36 (58) 0.0005 15 (24) 32 (52) 15 (24) 0.02
VAS, visual analog scale; NRS, numeric rating scale. *Including one responder who preferred a combination of VAS and NRS.
pain scale-revisited (FPS-R).2,6–10 Furthermore, some studies have indicated that VAS may not always be normally distributed.6,7 However, it is unknown how the VAS should optimally be applied, horizontally, vertically, and with or without endpoints. Previous research has shown that VAS vertical was the recommended form, in that it supposedly would be easier for the patient with sight impairment to see especially if anchors are read to the subject or typed in larger types.3 We did not ask our patients about sight impairment, and our patient sample represented the daily clinical patient population in large hospital wards in an urban area. Other studies have shown that when VAS was presented as a vertical line, patients would grade themselves higher.2,5,7 This is, however, not
without some form of uncertainty, as research has shown that the reading direction did impact the grading of pain given by a group of test subjects.7 In that manner, it was discovered that among a group of Chinese-speaking test subjects, a tendency existed to grade pain at a higher level when presented with a VAS horizontal, and just opposite, a group of Englishspeaking test subjects graded themselves higher when presented with a VAS vertical.11 However, in the present study, we did not find significant differences in mean scores between the four VAS measures. In many research cases, NRS has been seen as an easier way of grading pain, as opposed to using VAS.2,6,9 Thus, verbal denomination of pain intensity is preferred by patients, compared with using visual tools for measuring the intensity of pain.2,9,11,12 The patients in the current study who preferred NRS explained that they felt it was a more accurate way of stating the level of pain as a numeric value and felt more secure in verbally delivering the level of pain the patients were experiencing to the clinician, as opposed to visualizing the sensation. We found a tendency toward higher NRS scores when patients had low mean pain scores, whereas the scores seemed similar when patients had high mean scores. Despite a set of scientific studies having compared the most popular pain-grading tools VAS, NRS, and the VRS,3,4,6,9–19 in none of the cases were the different usages of VAS questioned in regard to grading pain, even though a study13 had uncovered potential flaws in the different usages/formats of VAS being applied. This fact
Patient Pain Measurement Preference 5
obviously questions the outcome of previous comparisons performed on different pain-grading tools. Our study has some limitations. As the selected sample size for the study was set to only include postoperative patients in a state of rest, one could dispute that no consideration was given for the high fluctuations often seen when patients are moving or coughing after surgery. As the study did not intend to observe the different levels of pain, but rather how it was graded in order to find a preferred form/method, it was deliberately not taken into account in this study to investigate the differences which might exist between rest and movement. Future studies should focus on this issue.
CONCLUSION Levels of pain were almost similar when measuring with the four different VAS methods and the NRS, but with the NRS giving slightly higher values especially at low pain levels. Patients preferred the NRS or the VAS horizontal including stop lines at the ends. Half of the patients explained that the dialog with a clinician and also a lack of visual overview were the primary factors for not having VAS as the preferred form as a means for grading pain compared to NRS. In the clinical setting, and based on our findings, it would be reasonable to recommend the use of a horizontal VAS with endpoints or an NRS. It may be easier for the frail patient to understand the NRS, so NRS could be used for daily clinical practice and perhaps the VAS reserved for research studies, where a more detailed scale often would be preferred.
REFERENCES 1. Wewers ME, Lowe NK. A critical review of visual analogue scales in the measurement of clinical phenomena. Res Nurs Health. 1990;13:227–236. 2. Rauh KH, Andersen RS, Rosenberg J. [Visual analogue scale for measuring post-operative pain]. Ugeskr Laeger. 2013;175:1712–1716. 3. Gift AG. Visual analogue scales: measurement of subjective phenomena. Nurs Res. 1989;38:286–288. 4. DeLoach LJ, Higgins MS, Caplan AB, Stiff JL. The visual analog scale in the immediate postoperative period: intrasubject variability and correlation with a numeric scale. Anesth Analg. 1998;86:102–106.
5. Scott J, Huskisson EC. Vertical or horizontal visual analogue scales. Ann Rheum Dis. 1979;38:560. 6. Lund I, Lundeberg T, Sandberg L, Budh CN, Kowalski J, Svensson E. Lack of interchangeability between visual analogue and verbal rating pain scales: a cross sectional description of pain etiology groups. BMC Med Res Methodol. 2005;5:1–9. 7. Williamson A, Hoggart B. Pain: a review of three commonly used pain rating scales. J Clin Nurs. 2005;14:798–804. 8. Hjermstad MJ, Fayers PM, Haugen DF, et al. Studies comparing numerical rating scales, verbal rating scales, and visual analogue scales for assessment of pain intensity in adults: a systematic literature review. J Pain Symptom Manage. 2011;41:1073–1093. 9. Ferreira-Valente MA, Pais-Ribeiro JL, Jensen MP. Validity of four pain rating scales. Pain. 2011;152:2399–2404. 10. Stephenson NL, Herman JA. Pain measurement: a comparison using horizontal and vertical visual analogue scales. Appl Nurs Res. 2000;13:157–158. 11. Jensen MP, Karoly P, Braver S. The measurement of clinical pain intensity: a comparison of six methods. Pain. 1986;27:117–126. 12. Gagliese L, Katz J. Age differences in postoperative pain are scale dependent: a comparison of measures of pain intensity and quality in younger and older surgical patients. Pain. 2003;103:11–20. 13. Aun C, Lam YM, Collett B. Evaluation of the use of visual analogue scale in Chinese patients. Pain. 1986;25:215–221. 14. Bijur PE, Latimer CT, Gallagher EJ. Validation of a verbally administered numerical rating scale of acute pain for use in the emergency department. Acad Emerg Med. 2003;10:390–392. 15. Bijur PE, Silver W, Gallagher EJ. Reliability of the visual analog scale for measurement of acute pain. Acad Emerg Med. 2001;8:1153–1157. 16. Salo D, Eget D, Lavery RF, Garner L, Bernstein S, Tandon K. Can patients accurately read a visual analog pain scale? Am J Emerg Med. 2003;21:515–519. 17. Jensen MP, Chen C, Brugger AM. Interpretation of visual analog scale ratings and change scores: a reanalysis of two clinical trials of postoperative pain. J Pain. 2003;4:407– 414. 18. Scott J, Huskisson EC. Accuracy of subjective measurements made with or without previous scores: an important source of error in serial measurement of subjective states. Ann Rheum Dis. 1979;38:558–559. 19. Lara-Mu~ noz C, Ponce de Leon S, Feinstein AR, Puente A, Wells CK. Comparison of three rating scales for measuring subjective phenomena in clinical research. I. Use of experimentally controlled auditory stimuli. Arch Med Res. 2004;35:43–48.
Preferred Presentation of the Visual Analog Scale for Measurement of Postoperative Pain Helle Birgitte Kjeldsen, RN*; Tobias Wirenfeldt Klausen, MS†; Jacob Rosenberg, DSc* *Department of Surgery, Herlev Hospital, Herlev; †Department of Hematology, Herlev Hospital, Herlev, Denmark
& Abstract Background: The aim of this study was to evaluate differences in pain scores with different visual analog scale (VAS) presentations and to compare those differences with a numeric rating scale. We also asked the patients for preference of the different methods. Methods: Prior to the trial, we performed power calculations to estimate a preferred sample size, and 62 postoperative patients supplied a complete set of data to the study. Inclusion criteria were newly operated patients within the first 5 days after surgery. Every patient included was with 1minute intervals and presented with one of the following 100-mm VAS lines: VAS horizontal with or without stop lines at the endings, or VAS vertical with or without stop lines. They also completed a numeric rating scale (NRS). Results: We did not find differences in pain scores between the four VAS measures. The NRS had slightly higher pain scores than VAS, especially at low levels of pain. Patients preferred the NRS as compared to the VAS, and when choosing between the four different VAS presentations, they preferred the horizontal VAS with stop lines at the ends. Conclusion: For daily clinical practice for guiding postoperative analgesic treatment, the NRS seems to be a good option measuring pain reliably with good patient understanding
Address correspondence and reprint requests to: Jacob Rosenberg, DSc, Department of Surgery, Herlev Hospital, Herlev Ringvej 75 Herlev 2730, Denmark. E-mail: [email protected]. Funding: The study did not receive any funding. Conflict of interest: The authors have no conflict of interest. Submitted: April 6, 2015; Revision accepted: June 17, 2015 DOI. 10.1111/papr.12344
© 2015 World Institute of Pain, 1530-7085/15/$15.00 Pain Practice, Volume , Issue , 2015 –
and acceptance. For pain research, where there may be more time to explain the method and when a scale with more data points may be preferred, a VAS horizontal including stop lines at the ends can be recommended. & Key Words: pain, postoperative, visual analog scale, numeric rating scale, patient preference
INTRODUCTION The visual analog scale (VAS) has been used for measuring both acute and chronic pain since 1966.1,2 Measurement of unpleasant, subjective phenomena such as nausea, fatigue, dyspnea, and pain are experiences that require self-report.3 VAS is a simple and often used paingrading tool to measure such subjective symptoms.1,3 Commonly, a VAS is formed as a 100-mm horizontal line, and in this form, it has been shown to produce a more uniform distribution of pain scores than a vertical VAS.1 Patients are instructed to grade the pain intensity by marking a 100-mm line anchored with terms describing the extremes of the intensity of pain.4 Studies have found that the pain scores from the horizontal scale tended to be slightly lower than that from the vertical scale.5 Therefore, the application of VAS is ambiguous, as it has been shown that different methods of applying VAS are being used: VAS vertical, with and without endpoints; VAS horizontal, with and without endpoints; and to a further extent, up to 24 different adjectives have been used describing the extremes at the VAS lines. Commonly, the adjectives chosen are in some form of “no pain” and “worst imaginable pain”.2,4
2
KJELDSEN ET AL.
The aim of the study was to evaluate whether patients would grade themselves differently, depending on which VAS presentation/form was used and which presentation the patients preferred.
METHODS All patients 1 to 5 days after operation in the departments of surgery, gynecology, and orthopedic surgery, and those fulfilling the inclusion criteria were screened for candidacy during March 2014. Inclusion criteria were newly operated patients within the first 5 days after surgery, informed consent, and age > 18 years. Exclusion criteria were prior participants, linguistic challenges, or whether the patients were physically or mentally unstable to an extent that they could not understand the research question. Every patient included was with 1-minute intervals and presented with one of the following 100-mm VAS lines: VAS horizontal with or without stop lines at the endings, or VAS vertical with or without stop lines (Figure 1). With one stroke across the VAS line, the patient was asked to indicate the level of pain currently perceived in a state of rest. When the patient had indicated the current pain sensation on all four VAS lines, the patient was also asked to give a numerical representation of the pain sensation, on a scale ranging from 1 to 10 (corresponding to NRS) in a state of rest. Finally, the interviewer would ask the patient what the preferred method of pain grading had been. To this, the patient was presented with three scenarios: VAS horizontal vs. VAS vertical, VAS with endpoints vs. VAS without endpoints, and VAS vs. NRS. To each answer, the patient was allowed to answer one of the two or “indifferent”. The patient was asked to provide a
Worst pain imaginable
No pain
Worst pain imaginable
No pain
Worst pain imaginable
No pain
comment for the choices he/she had made. The orders of the four VAS lines were randomized using a randomization generator (www.randomization.com). The randomization generator created a random permutation of the four VAS lines, to assure that all candidates received the four VAS lines in random order (Figure 1). The study was approved by the Danish Data Protection Agency (HEH-2014-054) and was posted on www.clinicaltrials.gov (NCT02243410). The study was exempted for approval by the local ethics committee because it was regarded as a quality assurance study without biomedical interventions (H-4-2014-fsp). All patients participated after providing an informed consent. Prior to the trial, we performed power calculations to estimate a preferred sample size. From an expected intraclass correlation (ICC) of 0.8, it would require a sample size of 61, to gain an 80% certainty of having a lower boundary of 95% and a confidence interval above 0.65. In total, 62 postoperative patients supplied a complete set of data to the study. Agreement between different VAS scores and NRS score was inspected using ICC and Bland–Altman plots. Differences in values between scores were analyzed using paired t-test or repeated-measures ANOVA. Patient preferences were analyzed using frequencies, and significance were analyzed by comparison of preference in one direction vs. the other direction using a binomial test with a 50% reference ignoring neutral answers. All tests were two sided. P < 0.05 was regarded as statistically significant, and limits of confidence were 95%. All statistics was performed using SPSS version 19.0 (IBM corp., Armonk, NY, U.S.A.) or R version 3.1.0 (R Foundation for Statistical Computing, Vienna, Austria).
Worst pain imaginable
No pain
Figure 1. All four visual analog scale (VAS) lines used in the research were 10 cm in actual length.
Patient Pain Measurement Preference 3
RESULTS Two patients had major internal disagreements that indicated a general misconception of the VAS lines. We excluded these patients from the analyses except for the analyses of patient preferences. A sensitivity analysis was performed to inspect whether the inclusion of these patients would generate different conclusions. We did not find different results including these patients. High levels of agreement were found between all five measures. Intraclass correlation coefficients were in the range of 0.93 to 0.98, and all comparisons had lower limits of confidence intervals above 0.8. NRS had equal agreement between the VAS scores as VAS scores had between each other, and we did not find any pattern in the values. Results are shown in Table 1. We did not find differences in mean scores between the four VAS measures (P = 0.5). The NRS had significantly higher mean scores than all VAS scores. Mean differences were 0.42 (95% CI: 0.19; 0.66, P = 0.0007), 0.51 (95% CI: 0.27; 0.74, P < 0.0001), 0.37 (95% CI: 0.14; 0.60, P = 0.002), and 0.36 (95% CI: 0.11; 0.62, P = 0.006). Results are shown in Table 2. In a Bland– Altman plot (Figure 2) comparing the difference between NRS and VAS (horizontal and including end lines), we saw a tendency toward higher NRS scores when patients had low mean pain scores, whereas the scores seemed similar when patients had high mean
scores. Patients with a mean score below 5 had a mean difference at 0.64 and those with a mean score above 5 had a mean difference at 0.31 (P = 0.0004). Of 62 patients, 22 patients (35%) had a preference toward VAS horizontal compared to VAS vertical 9 (15%) (P = 0.04). Thirty-two patients (52%) were neutral. Results are shown in Table 3. As a further notion, 22 (35%) patients voiced that it was easier to understand VAS with endpoint compared to 4 (6%) patients preferring VAS without endpoints (P = 0.0005), though 36 (58%) patients were neutral. Of the 62 participants, 32 (52%) had NRS as the preferred means and 15 (24%) had VAS as their preferred (P = 0.02), with 15 (24%) patients being neutral.
DISCUSSION We found that the different VAS scores were similar, but the NRS had slightly higher scores than all VAS scores, mainly if pain levels were low. Patient preference pointed at the horizontal VAS with endpoints or the NRS for the measurement of postoperative pain. Multiple studies have described the differences found between the existing pain-grading tools, which are most commonly used among clinicians and researchers.6–8 These entail the visual analog scale (VAS), numerical rating scale (NRS), verbal rating scale (VRS), and faces
Table 1. Intraclass Correlation Coefficients (ICC) Between the Five Measures
VAS VAS VAS VAS NRS
horizontal with endpoints horizontal without endpoints vertical with endpoints vertical without endpoints
VAS Horizontal with Endpoints
VAS Horizontal Without Endpoints
VAS Vertical with Endpoints
VAS Vertical Without Endpoints
– 0.97 0.97 0.93 0.94
– 0.98 (0.97; 0.99) 0.96 (0.93; 0.98) 0.94 (0.85; 0.97)
– 0.97 (0.95; 0.98) 0.95 (0.90; 0.97)
– 0.94 (0.88; 0.96)
(0.95; (0.95; (0.89; (0.88;
0.98) 0.98) 0.96) 0.97)
Table shows ICC, including 95% confidence limits. VAS, visual analog scale; NRS, numeric rating scale.
Table 2. Comparisons Between Mean Scores VAS Comparison
VAS VAS VAS VAS NRS
horizontal with endpoints horizontal without endpoints vertical with endpoints vertical without endpoints
Mean (SD)
Mean Difference (95% CI)
3.05 2.96 3.10 3.11 3.47
Reference value 0.08 ( 0.27; 0.10) 0.05 ( 0.15; 0.25) 0.06 (0.22; 0.34) –
(2.98) (2.86) (3.04) (2.99) (2.79)
Overall P for VAS comparison: P = 0.5; overall P for NRS-VAS comparison: P < 0.0001. VAS, visual analog scale; NRS, numeric rating scale.
NRS-VAS Comparison P – 0.4 0.6 0.7 –
Mean Difference (95% CI) 0.42 ( 0.66; 0.19) 0.51 ( 0.74; 0.27) 0.37 ( 0.60; 0.14) 0.36 ( 0.62; 0.11) Reference value
P 0.0007 < 0.0001 0.002 0.006 –
4
KJELDSEN ET AL.
Figure 2. Bland–Altman plot of the difference between numeric rating scale (NRS) and visual analog scale (VAS) plotted against the mean of NRS and VAS. The three lines represent average difference (solid line) and 95% limits of agreement (1.96 SD).
Table 3. Patient Preferences N (%) VAS horizontal vs. vertical Horizontal preferred Vertical preferred Neutral or no opinion P Endpoints Endpoints preferred No endpoints preferred Neutral or no opinion P VAS vs. NRS VAS preferred NRS preferred Neutral or no opinion* P
21 (34) 9 (15) 32 (52) 0.04 22 (35) 4 (6) 36 (58) 0.0005 15 (24) 32 (52) 15 (24) 0.02
VAS, visual analog scale; NRS, numeric rating scale. *Including one responder who preferred a combination of VAS and NRS.
pain scale-revisited (FPS-R).2,6–10 Furthermore, some studies have indicated that VAS may not always be normally distributed.6,7 However, it is unknown how the VAS should optimally be applied, horizontally, vertically, and with or without endpoints. Previous research has shown that VAS vertical was the recommended form, in that it supposedly would be easier for the patient with sight impairment to see especially if anchors are read to the subject or typed in larger types.3 We did not ask our patients about sight impairment, and our patient sample represented the daily clinical patient population in large hospital wards in an urban area. Other studies have shown that when VAS was presented as a vertical line, patients would grade themselves higher.2,5,7 This is, however, not
without some form of uncertainty, as research has shown that the reading direction did impact the grading of pain given by a group of test subjects.7 In that manner, it was discovered that among a group of Chinese-speaking test subjects, a tendency existed to grade pain at a higher level when presented with a VAS horizontal, and just opposite, a group of Englishspeaking test subjects graded themselves higher when presented with a VAS vertical.11 However, in the present study, we did not find significant differences in mean scores between the four VAS measures. In many research cases, NRS has been seen as an easier way of grading pain, as opposed to using VAS.2,6,9 Thus, verbal denomination of pain intensity is preferred by patients, compared with using visual tools for measuring the intensity of pain.2,9,11,12 The patients in the current study who preferred NRS explained that they felt it was a more accurate way of stating the level of pain as a numeric value and felt more secure in verbally delivering the level of pain the patients were experiencing to the clinician, as opposed to visualizing the sensation. We found a tendency toward higher NRS scores when patients had low mean pain scores, whereas the scores seemed similar when patients had high mean scores. Despite a set of scientific studies having compared the most popular pain-grading tools VAS, NRS, and the VRS,3,4,6,9–19 in none of the cases were the different usages of VAS questioned in regard to grading pain, even though a study13 had uncovered potential flaws in the different usages/formats of VAS being applied. This fact
Patient Pain Measurement Preference 5
obviously questions the outcome of previous comparisons performed on different pain-grading tools. Our study has some limitations. As the selected sample size for the study was set to only include postoperative patients in a state of rest, one could dispute that no consideration was given for the high fluctuations often seen when patients are moving or coughing after surgery. As the study did not intend to observe the different levels of pain, but rather how it was graded in order to find a preferred form/method, it was deliberately not taken into account in this study to investigate the differences which might exist between rest and movement. Future studies should focus on this issue.
CONCLUSION Levels of pain were almost similar when measuring with the four different VAS methods and the NRS, but with the NRS giving slightly higher values especially at low pain levels. Patients preferred the NRS or the VAS horizontal including stop lines at the ends. Half of the patients explained that the dialog with a clinician and also a lack of visual overview were the primary factors for not having VAS as the preferred form as a means for grading pain compared to NRS. In the clinical setting, and based on our findings, it would be reasonable to recommend the use of a horizontal VAS with endpoints or an NRS. It may be easier for the frail patient to understand the NRS, so NRS could be used for daily clinical practice and perhaps the VAS reserved for research studies, where a more detailed scale often would be preferred.
REFERENCES 1. Wewers ME, Lowe NK. A critical review of visual analogue scales in the measurement of clinical phenomena. Res Nurs Health. 1990;13:227–236. 2. Rauh KH, Andersen RS, Rosenberg J. [Visual analogue scale for measuring post-operative pain]. Ugeskr Laeger. 2013;175:1712–1716. 3. Gift AG. Visual analogue scales: measurement of subjective phenomena. Nurs Res. 1989;38:286–288. 4. DeLoach LJ, Higgins MS, Caplan AB, Stiff JL. The visual analog scale in the immediate postoperative period: intrasubject variability and correlation with a numeric scale. Anesth Analg. 1998;86:102–106.
5. Scott J, Huskisson EC. Vertical or horizontal visual analogue scales. Ann Rheum Dis. 1979;38:560. 6. Lund I, Lundeberg T, Sandberg L, Budh CN, Kowalski J, Svensson E. Lack of interchangeability between visual analogue and verbal rating pain scales: a cross sectional description of pain etiology groups. BMC Med Res Methodol. 2005;5:1–9. 7. Williamson A, Hoggart B. Pain: a review of three commonly used pain rating scales. J Clin Nurs. 2005;14:798–804. 8. Hjermstad MJ, Fayers PM, Haugen DF, et al. Studies comparing numerical rating scales, verbal rating scales, and visual analogue scales for assessment of pain intensity in adults: a systematic literature review. J Pain Symptom Manage. 2011;41:1073–1093. 9. Ferreira-Valente MA, Pais-Ribeiro JL, Jensen MP. Validity of four pain rating scales. Pain. 2011;152:2399–2404. 10. Stephenson NL, Herman JA. Pain measurement: a comparison using horizontal and vertical visual analogue scales. Appl Nurs Res. 2000;13:157–158. 11. Jensen MP, Karoly P, Braver S. The measurement of clinical pain intensity: a comparison of six methods. Pain. 1986;27:117–126. 12. Gagliese L, Katz J. Age differences in postoperative pain are scale dependent: a comparison of measures of pain intensity and quality in younger and older surgical patients. Pain. 2003;103:11–20. 13. Aun C, Lam YM, Collett B. Evaluation of the use of visual analogue scale in Chinese patients. Pain. 1986;25:215–221. 14. Bijur PE, Latimer CT, Gallagher EJ. Validation of a verbally administered numerical rating scale of acute pain for use in the emergency department. Acad Emerg Med. 2003;10:390–392. 15. Bijur PE, Silver W, Gallagher EJ. Reliability of the visual analog scale for measurement of acute pain. Acad Emerg Med. 2001;8:1153–1157. 16. Salo D, Eget D, Lavery RF, Garner L, Bernstein S, Tandon K. Can patients accurately read a visual analog pain scale? Am J Emerg Med. 2003;21:515–519. 17. Jensen MP, Chen C, Brugger AM. Interpretation of visual analog scale ratings and change scores: a reanalysis of two clinical trials of postoperative pain. J Pain. 2003;4:407– 414. 18. Scott J, Huskisson EC. Accuracy of subjective measurements made with or without previous scores: an important source of error in serial measurement of subjective states. Ann Rheum Dis. 1979;38:558–559. 19. Lara-Mu~ noz C, Ponce de Leon S, Feinstein AR, Puente A, Wells CK. Comparison of three rating scales for measuring subjective phenomena in clinical research. I. Use of experimentally controlled auditory stimuli. Arch Med Res. 2004;35:43–48.
