Data were extracted on sample characteristics, assessment methods, statistical analysis, outcome measures, and study quality. (ebmh.bmj.com)
Such studies should also address the comparison of data sets with different sampling characteristics. (nap.edu)
This may be explained by differences in sample characteristics like differences in age and sexual orientation or cultural differences between Northern European countries such as the Netherlands and other Western countries (van den Brink et al., 2013). (link.springer.com)