De praktijk van systematische reviews. V. Heterogeniteit tussen onderzoeken en subgroepanalysen

- Meta-analysis comprises the analysis of the data of similar studies gathered in a systematic review.

- If the results of the studies differ (strongly), this is called heterogeneity.

- Possible causes of heterogeneity are: a wrong choice of type of measure of treatment effect, differences of methodological quality between studies, or real differences between studies.

- Heterogeneity between studies can be assessed by thorough examination of the differences between study characteristics in combination with a visual inspection of the degree of overlap of the confidence intervals of the estimates of effect of the different studies.

- By applying the random effects model for pooling, (non-systematic) heterogeneity between studies can be addressed.

- In case of heterogeneity between studies, sources of heterogeneity should be explored by means of subgroup analysis according to strict, preset criteria.

- Subgroup analysis should address subgroups of patients within studies.