Study design and samples
A convenience sample of 124 older patients undergoing
elective abdominal surgery between April 2011 and
December 2011 were recruited from general surgical
wards of a university teaching hospital in Tehran and
enrolled in a randomized controlled trial (RCT). The
RCT is a classic and precise method for examining the
effects of an independent variable on a dependent one by
comparing them in experimental and control groups.28
The sample size of 62 participants per group was achieved
based on a power analysis for the covariance using a
moderate effect size, power of 0.90 and a = 0.05. Two
patients dropped out of each group due to transfer of ward
or surgery cancellation.