7.3.2  Methods and potential sources of bias

Different research methods can influence study outcomes by introducing different biases into results. Basic study design characteristics should be collected for presentation in the table of ‘Characteristics of included studies’, including whether the study is randomized, whether the study has a cluster or cross-over design, and the duration of the study. If the review includes non-randomized studies, appropriate features of the studies should be described (see Chapter 13, Section 13.4).


Information should also be collected to facilitate assessments of the risk of bias in each included study using the tool described in Chapter 8 (Section 8.5). The tool covers issues such as sequence generation, allocation sequence concealment, blinding, incomplete outcome data and selective outcome reporting. For each item in the tool, a description of what happened in the study is required, which may include verbatim quotes from study reports. Information for assessment of incomplete outcome data and selective outcome reporting may be most conveniently collected alongside information on outcomes and results. Chapter 8 (Section 8.3.4) discusses some issues in the collection of information for assessments of risk of bias.