ABSTRACT
The standard error of the mean (SEM) is a margin of error that is used when estimating the population mean from a sample drawn at random from a population. The 95" confidence interval is based on the standard error of the mean. When a 95" confidence interval for a mean is reported, it means that if the study were replicated, 95" of the time the mean would fall within the 95" CI. The standard error of the mean is inversely related to the number of participants in a sample or group. So the larger the group, the smaller the standard error of the mean. This chapter examines post-traumatic stress disorder (PTSD) symptoms pre- and post-[treatment] for a large sample of male and female veterans treated in the same setting as part of routine care, with appropriate power to find clinically relevant differences between.
