There were 8 methodological criteria on which the studies were rated:
clear definition of aims;
a description of the intervention package and design sufficiently detailed to allow replication;
inclusion of a randomly allocated control group;
provision of data on number of participants recruited to study and control groups;
provision of pre-intervention data for the study and control groups;
provision of post-intervention data for the study and control groups;
attrition rates reported for the study and control groups; and
findings reported for each outcome measure as described in the aims of the study.
Sound studies were those meeting the following criteria: inclusion of a control group, pre- and post-test intervention data, and information on all relevant outcomes. Two reviewers with backgrounds in quantitative social science independently assessed each study. Disagreements were discussed and resolved with a third reviewer.