Table 1.

The tool used to rate the quality of the included studies

Quality assessment criteria	Score
1) Aims/objectives of the study clearly stated	1
2) Definition of what constitutes a DDI	1
3) DDI categories specified	1
4) DDI categories defined	1
5) Mention of DDI reference	1
6) Data collection method described clearly	1
7) Setting in which study was conducted described	1
8) Study subjects described	1
9) Sampling and calculation of sample size described (unit of measurement)	1
10) Potential or actual DDIs assessed	1
11) Measures in place to ensure that results are valid	1
12) Limitations of study listed	1
Maximum score	12 points

Each item is related to a quality assessment criterion with score 0 or 1.