Table 3 Maryland Scientific Methods Scale interpreted to suit the studies under review
Internal validity | Description |
|---|---|
Level I | Correlation analysis, no control group nor attempt to establish counterfactual |
Level II | ‘Before & after comparison’ or comparison group without balancing covariates |
Level III | Difference in Difference, attempt at balancing (OLS, matching) but uncontrolled differences likely remain |
Level IV | Explicitly reasoned and proper balancing (OLS, matching), biases discussed but not addressed |
Level V | RCTs, no selective sample attrition |