The use of survival analysis for the evaluation of musculoskeletal therapy.

urvival analysis is seldom used in studies of the S of musculoskeletal therapy. Most clinical studies of musculoskeletal therapy use parametric statistical methods such as analysis of variance (ANOVA) to illustrate the effects of treatment on outcomes. Nonparametric techniques of analysis such as survival analysis are less frequently used. Survival analysis has a number of advantages that make a research design a better choice than ANOVA for clinical evaluation studies. Among these advantages are that survival analysis uses a patient-specific response as an output measure whereas ANOVA requires the valid generation of a group mean response. Comparison of the results of studies is clear and unambiguous with survival analysis, which produces a survival function that represents the effect of treatment over the entire course of the study. Comparison of the results of studies is difficult with ANOVA, which produces estimates of effectiveness at a few discrete points during the study. Survival analysis is bdistribution freeQ and enables the direct analysis of highly skewed distributions that are commonly encountered in studies where patients respond as individuals to treatment and do not require data transformations to meet the underlying assumptions of parametric statistical methods such as ANOVA. Lastly, survival analysis incorporates a method of explicitly dealing with the problem of incomplete observations, which is not available in ANOVA. Analysis of variance is used to study the mean values of 2 populations, often the distribution of some measure of response to treatment. Analysis of variance is termed a parametric method of analysis because it depends on the calculation of parameters of the distribution of measures of interest such as the mean and standard deviation. Analysis of variance is based on the mathematical concept of least squares. The least squares formulation requires that each incidence of the measure of response be subtracted from the