SPIDER (Sample, Phenomenon of Interest, Design, Evaluation, Research type) framework for inclusion and exclusion criteria
| SPIDER framework | Inclusion criteria | Exclusion criteria |
| Sample | Sample size and characteristics were not a criterion for inclusion in this review Age 18 years or older | Sample size and characteristics were not a criterion for exclusion in this review Age less than 18 years |
| Phenomenon of Interest | Adult mortality according to educational attainment All-cause mortality | Indices using education aggregated with other indicators Cause-specific mortality |
| Design | All study designs other than the two listed in exclusion criteria | Case-crossover and ecological studies |
| Evaluation | Individual-level measures Relative inequality measures: relative risk, HR, OR, rate ratio, logistic coefficients | Aggregate-level measures Measures: Standardised incidence ratio, standardised mortality ratio, time-to-event ratio, incidence, rate and risk difference |
| Publication type | Publication type is not an inclusion criterion | Comment, editorials or letters |