All subscales were transformed to a 0 to 100 scale, with higher scores indicting better functioning, and five points “defines differences that are clinically and socially relevant” (Ware et al., 1993). In general, physical-, role-, and social-functioning subscales capture behavioral dysfunctioning caused by health problems. The dimensions of overall health, bodily pain, and particularly mental health reflect more subjective components of health and general-welling (Stewart et al., 1989). The consistency estimates of the four multi-item SF-20 measures varied from .77 (physical functioning) to .89(mental health) for Week 1, .78 to .88 for Week 12, and .79 to .86 for Week 24.

Procedures
All participants completed the measures described previously during an initial group orientation meeting (Week 1). Before beginning, participants signed consent forms, indicating the voluntary and anonymous nature of the study. Instructions were read aloud by the researcher, and sample questions were provided prior to the administration of the questionnaire. Additionally, participants were encouraged to clarify any questions/confusions they might have with regard to the questionnaire. No problems were encountered with participants understanding the questions or completing the questionnaire.
Participants from the experimental group completed these measures a second (Week 12) and third (Week 24) time either at the end of class or at home within a week interval. Participants in the control group completed their second and third assessments by mail. Trained research assistants in compliance with institutional review board procedures for studies involving human subjects, administered the survey measures.

Program Compliance
From the initial sample of 94 participants, seventy-two completed all assessments. Nine participants in the Tai Chi group (18% attrition rate) dropped out of the study for reasons such as traveling and family-related commitments. Thirteen participants dropped out of the control group (29% attrition rate) because of unwillingness to wait for the Tai Chi class offered at the end of the study. Thus, the total attrition rate at the end of the study was 23%. Class attendance was recorded for each subject in the experimental group. The average attendance rate (2 times/per week, a total of 48 possible sessions) in the Tai Chi group was approximately 90% with a median compliance of 41 sessions, and ranging from 29 to 47 sessions. Reasons for missing sessions included inclement weather, holidays, and family commitments.

Statistical Analyses
Before conducting the primary analyses of the study, we examined whether attrition influenced the representativeness of the remaining subject sample and whether the experimental participants were different on demographic variables that were not controlled in the random assignment procedure. All tests were completed using the analysis of variance (ANOVA) procedure. Following these preliminary tests, repeated measures ANOVA procedures (with Group as a between-subjects factor and Time as a within-subject factor) were used to examine changes over time and differences between Tai Chi and control groups. An interaction between Group and Time indicated a difference in group responses on HRQL measures, suggesting a treatment effect. The primary outcomes (dependent variables) analyzed were the six dimensions of SF-20. Statistical significance was defined as a P value of less than .05; all P values are two-tailed.