When a clinical trial is planned, the approximate number of subjects needed for significant differences between/among groups to be detected must be estimated. Sample-size calculations provide the investigator with this information.
This paper discusses the choice of outcome measures and describes the steps used to estimate the numbers of subjects necessary for a study that compares treatments for patients with chronic myofascial pain of jaw muscles. Within- and between-subject variances were estimated for the chosen variables, the subjects' pain ratings on visual analogue scales. Sample sizes were then calculated for theoretical differences between groups by pre-treatment means and overall standard deviations (Cohen, 1977).
The results of this analysis can be used by other researchers when planning studies involving these types of patients.
Get full access to this article
View all access options for this article.
References
1.
Altman, D.G. (1980): Statistics and Ethics in Medical Research. III. How Large a Sample?, Br Med J281:1336-1338.
2.
Bell, W.D. (1982): Classification of TM Disorders. In: The President's Conference on the Examination, Diagnosis and Management of Temporomandibular Disorders, D. Laskin, W. Greenfield, E. Gale , J. Rugh, P. Neff, C. Alling, and W.A. Ayer, Eds., Chicago: American Dental Association, pp. 24-29.
3.
Bell, W.D. (1990): Temporomandibular Disorders. Classification, Diagnosis, Management, 3rd ed., Chicago : Yearbook Medical Publishers.
4.
Clark, G.T.; Lanham, F.; and Flack, V.F. (1988): Treatment Outcome Results for Consecutive TMJ Clinic Patients, J Craniomandib Disord2:87-95.
5.
Cohen, J. (1977): Statistical Power Analysis for the Behavioral Sciences, New York: Academic Press .
6.
Cooper, B.C. and Rabuzzi, D.D. (1984): Myofacial (sic) Pain Dysfunction Syndrome: A Clinical Study of Asymptomatic Subjects, Laryngoscope94:68-75.
Duncan, G.H.; Bushnell, M.C.; and Lavigne, G.J. (1989): Comparison of Verbal and Visual Analogue Scales for Measuring the Intensity and Unpleasantness of Experimental Pain, Pain37 :295-303.
9.
Ekblom, A. and Hansson, P. (1988): Pain Intensity Measurements in Patients with Acute Pain Receiving Afferent Stimulation, J Neurol Neurosurg Psychiat51:481-486.
10.
Feine, J.S.; Dao, T.T.T.; Lavigne, G.J.; and Lund, J.P. (1989): Is Treatment Success due to Faulty Memory of Chronic Pain?, J Dent Res68 (Sp Iss):1018, Abst. No. 1207.
11.
Freiman, J.A.; Chalmers, T.C.; Smith, H.; and Kuebler, R.R. (1978): The Importance of Beta, the Type II Error and Sample Size in the Design and Interpretation of the Randomized Control Trial , N Engl J Med299:690-694.
12.
Friedman, L.M.; Furberg, C.D.; and Demets, D.L. (1985): Fundamentals of Clinical Trials, Littleton: PSG Publishing Company.
13.
Goldstein, H. (1979): The Design and Analysis of Longitudinal Studies , London: Academic Press.
14.
Goldstein, H. (1987): Multilevel Models in Educational and Social Research , London: Griffin.
Greene, C.S. and Laskin, D.M. (1983): Long-term Evaluation of Treatment for Myofascial Pain-Dysfunction Syndrome: a Comparative Analysis, J Am Dent Assoc107:235-238.
17.
Griffiths, R.H. (1983): Report of the President's Conference on the Examination, Diagnosis, Management of Temporomandibular Disorders, J Am Dent Assoc106:75-77.
18.
Harkins, R.; Marteney, J.L.; Cueva, O.; and Cueva, L. (1988): Application of Soft Occlusal Splints in Patients Suffering From Clicking Temporal Mandibular Joints, Cranio6:72-76.
19.
Hulley, S.B. and Cummings, S.R. (1988): Designing Clinical Research, Baltimore: Williams and Wilkins.
20.
Jamison, R.N.; Sbrocco, T.; and Parris, W.C.V. (1989): The Influence of Physical and Psychosocial Factors on Accuracy of Memory for Pain in Chronic Pain Patients, Pain37:289-294.
21.
Jankelson, R. and Pulley, M.L. (1984): Electromyography in Clinical Dentistry, Seattle: Myotronics Research, Inc.
22.
Lachin, J.M. (1981): Introduction to Sample Size Determination and Power Analysis for Clinical Trials, Controlled Clin Trials2:93-113.
23.
Linton, S.J. and Gotestam, K.G. (1983): A Clinical Comparison of Two Pain Scales: Correlation, Remembering Chronic Pain, and a Measure of Compliance, Pain17:57-65.
24.
Linton, S.J. and Melin, L. (1982): The Accuracy of Remembering Chronic Pain, Pain13:281-285.
25.
Lund, J.P.; Widmer, C.G.; and Schwartz, G. (1989): What is the Link Between Myofascial Pain and Dysfunction? In: Electromyography of Jaw Reflexes in Man, D. van Steenberghe and A. DeLaat, Eds., Leuven: Leuven University Press, pp. 427-444.
26.
McNeill, C. (1990): Craniomandibular Disorders-Guidelines for Evaluation, Diagnosis, and Management, Chicago: Quintessence.
27.
Medical Research Council Of Canada (1987): MRC Guidelines on Research Involving Human Subjects, Ottawa : Supply and Services Canada (MR 21-5/1987).
28.
Mohl, N.D.; Lund, J.P.; Widmer, C.G.; and McCall, W.D. (1990a): Devices for the Diagnosis and Treatment of Temporomandibular Disorders. Part II: Electromyography and Sonography, J Prosthet Dent63:332-336.
29.
Mohl, N.D.; McCall, W.D.; Lund, J.P.; and Plesh, O. (1990b): Devices for the Diagnosis and Treatment of Temporomandibular Disorders. Part I: Introduction, Scientific Evidence, and Jaw Tracking, J Prosthet Dent63:198-201.
30.
Moller, E.; Sheikholeslam, A.; and Lous, I. (1984): Response of Elevator Activity During Mastication to Treatment of Functional Disorders, Scand J Dent Res92:64-83.
31.
Moore, P.A.; Duncan, G.H.; Scott, D.S.; Gregg, J.M.; and Ghia, J.N. (1979): The Submaximal Effort Tourniquet Test: its Use in Evaluating Experimental and Chronic Pain, Pain6 :375-382.
32.
Ohnhaus, E.E. and Adler, R. (1975): Methodological Problems in the Measurement of Pain: a Comparison Between the Verbal Rating Scale and the Visual Analogue Scale, Pain1:379-384.
33.
Price, D.D.; McGrath, P.A.; Rafii, A.; and Buckingham, B. (1983): The Validation of Visual Analogue Scales as Ratio Scale Measures for Chronic and Experimental Pain, Pain17 :45-56.
34.
Reed, J.F. and Slaichert, W. (1981): Statistical Proof in Inconclusive "Negative" Trials , Arch Intern Med141:1307-1310.
35.
Revill, S.I.; Robinson, J.O.; Rosen, M.; and Hogg, M.I.J. (1976): The Reliability of a Linear Analogue for Evaluating Pain, Anesthesia31:1191-1198.
36.
Rothman, K.J. (1986): Modern Epidemiology, Boston : Little, Brown.
37.
Rubinoff, M.S.; Gross, A.; and McCall, W.D. (1987): Conventional and Nonoccluding Splint Therapy Compared for Patients with Myofascial Pain Dysfunction Syndrome , Gen Dent (November-December) :502-506.
38.
Rugh, J.D. and Solberg, W.K. (1985): Oral Health Status in the United States: Temporomandibular Disorders, J Dent Educ49 :398-405.
39.
Schneiderman, M.A. (1964): The Proper Size of a Clinical Trial: "Grandma's Strudel" Method, J New Drug (Jan.-Feb.):3-11.
40.
Scott, J. and Huskisson, E.C. (1976): Graphic Representation of Pain, Pain2:174-184.
41.
Shields, J.M.; Clayton, J.A.; and Sindledecker, L.D. (1978): Using Pantographic Tracings to Detect TMJ and Muscle Dysfunctions, J Prosthet Dent39:80-87.
42.
Spriet, A. and Simon, P. (1985): Methodology of Clinical Drug Trials, New York: Karger.
43.
Sriwatanakul, K.; Kelvie, W.; Lasagna, L.; Calim-Lim, J.F.; Weis, O.F.; and Mehta, G.I. (1983): Studies with Different Types of Visual Analog Scales for Measurement of Pain, Clin Pharmacol Ther34:234-239.
44.
Van Willigen, J. (1979): The Sagittal Condylar Movements of the Clicking Temporomandibular Joint, J Oral Rehabil6:167-175.
45.
Widmer, C.G.; Lund, J.P.; and Feine, J.S. (1990): Evaluation of Diagnostic Tests for TMD, Calif Dent J18:53-60.
46.
Woodforde, J.M. and Merskey, H. (1972): Some Relationships between Subjective Measures of Pain, J Psychosom Res16:173-178.
47.
Young, M.J.; Bresnitz, E.A.; and Strom, B.L. (1983): Sample Size Nomograms for Interpreting Negative Clinical Studies, Ann Intern Med99:248-251.
