2.2. Sample size determination
A priori power calculations indicated that 27 patients
were needed in each group to detect a difference
in lumbar lordotic angle between the groups at 90%
power, a 5% significance level, a 2-tailed test, and an
expected effect size of d = 0.9 based on pilot research
consisted of 10 patients who received the same program
between June 1, 2009, and September 31, 2009.
The mean change and standard deviation were estimated
as 5.2 and 5.7, respectively. To account for high
drop-out rates, the sample size was increased by 40%