A scoping review finds that guides to authors of protocols for observational epidemiological studies varied highly in format and content.

Objective: To identify, characterize, and explore author guides on the role, format, and content of protocols for observational epidemiological studies, particularly cohort and case-control studies.

Study Design And Setting: Scoping review. We searched for guides in Medline, Embase, Google Scholar, 10 general medical and epidemiological/public health journals, and 10 major funders' websites. Two review authors extracted data. We classified guides as "main" based on word count and number of protocol items, described such guides more comprehensively and analyzed number of citations as an indicator of uptake.

Results: Thirty-nine protocol guides were included intended for cohort studies (n = 3), case-control studies (n = 1), or epidemiological studies in general (n = 35). Content and format were highly variable. Several guides had a broader focus than protocol development, e.g., also including study conduct and reporting. The guideline developmental process was often reported sparsely. One guide, intended for interventional studies, combined a systematic preparatory process with a primary focus on protocol development. We categorized seven guides as 'main'. In general the guides were cited infrequently, indicating limited uptake.

Conclusion: Guides for authors of protocols for observational epidemiological studies varied highly in format and content. We suggest that such guides should routinely be based on a systematic preparatory process.