Table 4.
Prediction of generic use*
| Benefit design scenario | Cost-sharing for a generic drug ($) | Cost-sharing difference ($) | Prior authorization | Step therapy | Predicted generic use |
|---|---|---|---|---|---|
| Antidepressants | |||||
| I | 7 | 26 | N | N | 75.3% |
| II | 7 | 33 | N | N | 77.1% |
| III | 5 | 26 | Y | Y | 81.9% |
| IV | 5 | 33 | Y | Y | 83.3% |
| Antidiabetics | |||||
| I | 7 | 26 | N | N | 79.0% |
| II | 7 | 33 | N | N | 80.4% |
| III | 4 | 26 | Y | Y | 83.0% |
| IV | 4 | 33 | Y | Y | 84.2% |
| Statins | |||||
| I | 7 | 25 | N | N | 55.9% |
| II | 7 | 32 | N | N | 58.9% |
| III | 5 | 25 | Y | Y | 64.6% |
| IV | 5 | 32 | Y | Y | 67.4% |
*
For each drug category, we calculated marginal effects of plan features on the use of generic drugs (Appendix B displays predicted generic use for all 16 scenarios in each drug category). We chose different combinations of the 25th and 75th percentiles of the cost-sharing for generic drugs, the 25th and 75th percentiles of the cost-sharing difference between brand and generic drugs, and whether or not prior authorization or step therapy was used. All covariates were adjusted for the predictions.