Table 4 Checklist for Reporting on Subgroup Analyses & Heterogeneity in Treatment Effects

• Report on the distribution of predicted risk (or risk score) in the study population overall and by treatment arm.

• Risk reporting should allow readers to assess the full distribution of the study population either graphically (e.g., histograms or box & whiskers plots) or by including information on the mean, standard deviation, median and interquantile ranges.

2. Primary subgroup analyses should include reporting how relative and absolute risk reduction varies in a risk-stratified analysis .

• The risk prediction model should be pre-specified (i.e., fully specified before any analysis of treatment-effect has begun) and preferably externally developed.

• Both absolute and relative risk reductions must be reported.

3. Any additional primary subgroup analysis should be pre-specified and limited to patient attributes with strong a priori pathophysiological or empirical justification .

• All primary subgroup comparisons must be pre-specified.

• Prespecification should include all aspects of the subgroup analysis, including threshold values for continuous or ordinal variables where these are used.

• All primary subgroup analyses must be justified based upon pathophysiological or empirical evidence that this factor modifies treatment effects.

4. Conduct and report on secondary (exploratory) subgroup analyses separately from primary subgroup comparisons .

• Secondary subgroup analyses must be reported separately from primary subgroup analyses and clearly labeled as exploratory (potential useful for hypothesis generation and informing future research, but having little or no immediate relevance to patient care).

5. All analyses conducted must be reported and statistical testing of HTE should be done using appropriate methods (such as interaction terms) and avoiding overinterpretation .

• Reporting must include results for all subgroup analyses conducted and the paper must state that primary subgroup analyses conducted were pre-specified and reported.

• Statistical comparisons should be limited to reporting for statistical significance of treatment heterogeneity between subgroups using interaction terms. (Testing for the significance of a treatment effect within a subgroup is inappropriate due to poor statistical power).

• Statistical comparisons should be corrected for the number of primary subgroup analyses performed.