abstract
- The calculation of sample size requires knowledge of the standard deviation (SD) of index variables. Unfortunately, there are no published lists of standard deviations and it is exceedingly difficult to locate variance estimates based on relevant populations. We used standardized procedures to determine in 60 patients with ankylosing spondylitis (AS) the SD of key outcome measures recommended in current Food Drug Administration and European League Against Rheumatism guidelines for AS clinical trials. We anticipate that these tables will be useful to clinical researchers in selecting outcome measures as well as for calculating sample size requirements for future clinical studies in AS.