| Case study | Study with <5 patients |
| Case-control study | An observational study comparing patients samples with matched controls |
| Clinical trial | Non-randomised comparative and single-arm clinical trials. |
| Cross-sectional study | Reports outcomes for a particular timepoint for a cohort |
| Economic evaluation or model | Assessing the costs, resource use or cost-effectiveness of treatments for cluster headache |
| Narrative review | Analysis and summary of topics related to productivity based on existing literature, with no systematic search for all relevant publications. |
| Prospective, observational | A cohort of patients are followed up over time, for example to assess the effects of a treatment |
| Randomised controlled trial | A study where patients are randomised to two or more treatment arms |
| Retrospective observational | Analysis of existing data from study participants that was collected in the past. |
| Single-arm clinical trial | Non-randomized prospective study assessing the outcomes associated with a single particular treatment |
| Study protocol | Study protocols from 2019 onwards where no results are yet available. |
| Systematic literature review | A study that identifies and collates data from all relevant publications on the topic based on a systematic search of the literature. |
| Unclear | Abstracts that don't have enough information for the study methodology to be clear |