Select patients with a specific diagnosis and treatment regime

[rosap]

Calculation of patients who start treatment as mono-therapy, dual-therapy, etc.:
- Calculation of patients with diabetes who start treatment as mono-therapy (metformin) or dual-therapy (metformin + sulphonylurea), etc;

[evank23]

Complicated cohort definitions (with other logical operators except OR for codes, say XOR or AND) to consider for future expansion. Currently not that common.