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Free STROBE Participant Flow Diagram Generator for Observational Studies

Generate the STROBE participant flow diagram for your cohort, case-control, or cross-sectional study. Live auto-calculation through enrolment, follow-up, and analysis stages. 300/600 dpi PNG and editable PowerPoint exports. No data leaves your browser.

In Simple Words: Observational studies — cohorts, case-control studies, and cross-sectional surveys — do not have the neat allocation diagram of a randomised trial. Instead they need a participant flow that shows how many people were in the source population, how many were assessed for eligibility, how many were enrolled, how many were followed up (in cohort studies), and how many were included in the final analysis. The STROBE statement (Strengthening the Reporting of Observational Studies in Epidemiology) provides the framework for this documentation.

This tool generates the STROBE participant flow with three sequential stages. Each stage feeds the next automatically — you enter the attrition at each step and the analysis count emerges. The diagram is structurally simpler than PRISMA or CONSORT. STROBE item 13c asks authors to consider using a flow diagram: it is recommended rather than mandatory, and some journals ask for one in their author instructions.

When to Use the STROBE Participant Flow Diagram

Use STROBE for any primary observational study: prospective cohort, retrospective cohort, case-control, and cross-sectional designs. STROBE applies to both clinical and epidemiological observational research. The participant flow diagram corresponds to STROBE checklist item 13 (study participants).

Do not use STROBE for systematic reviews — use PRISMA 2020. For meta-analysis of observational studies, use MOOSE. For statistical analysis of your observational data, see the odds ratio calculator or the Test Selector.

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Worked Examples

Example 1 — Prospective cohort of occupational asthma

A cohort study identified 1,000 workers from occupational health records as the source population. 200 did not meet inclusion criteria (wrong industry sector). 800 were assessed; 80 declined participation. 720 enrolled at baseline. During 5-year follow-up, 20 were lost (moved abroad, withdrew consent). 700 completed follow-up. 50 had insufficient biomarker data; 650 were included in the final analysis. Enter 1,000 assessed, 200 ineligible + 80 declined = 280 excluded, 720 enrolled, 20 lost, 50 excluded at analysis — the diagram auto-calculates 650 analysed.

Example 2 — Cross-sectional survey of hypertension prevalence

A cross-sectional survey of 1,500 adults sampled from a primary care register. 300 were excluded (age outside range, prior cardiovascular disease). 1,200 were invited to participate; 180 declined or did not respond. 1,020 were enrolled and completed the survey. There was no follow-up stage (cross-sectional design); all 1,020 with complete data were analysed. Enter 1,500 assessed, 300+180=480 excluded, 1,020 enrolled, 0 lost, 0 excluded at analysis — the diagram reflects the single-stage flow appropriate for cross-sectional studies.

Assumptions and Requirements

  • The flow covers your study design’s relevant stages. Cross-sectional studies typically skip the follow-up stage — enter 0 for lost-to-follow-up. Case-control studies have a different enrolment logic (cases and controls identified separately) — use the enrolment exclusions to document matching or control selection.
  • Exclusion reasons must reflect your actual eligibility criteria. STROBE item 6 requires your eligibility criteria to be stated in Methods; the flow diagram must be consistent with those criteria.
  • Attrition must be fully documented. Every person enrolled but not analysed must be accounted for. STROBE item 13 asks for the numbers at each stage and the reasons for non-participation; item 14b asks for the number of participants with missing data for each variable of interest.

Common Mistakes

  • Conflating the source population and the assessed-for-eligibility group. Your source population (e.g. hospital registry) may be much larger than those actually assessed for eligibility — document both if they differ.
  • Omitting the analysis exclusions. Even if everyone enrolled was followed up, participants may be excluded from analysis due to missing outcomes, protocol violations, or data quality issues. These must appear in the flow.
  • Mixing follow-up loss with analysis exclusions. Lost to follow-up (participants who did not complete the study) and excluded from analysis (participants whose data were not used) are distinct categories and must be documented separately.
  • Using STROBE for a meta-analysis. A meta-analysis of observational studies requires MOOSE — STROBE describes the flow for a primary observational study, not for a synthesis.

Frequently Asked Questions

Does STROBE require a participant flow diagram?
Not as a mandatory element. STROBE item 13 asks authors to (a) report numbers of individuals at each stage of study, e.g. numbers potentially eligible, examined for eligibility, confirmed eligible, included in the study, completing follow-up, and analysed; (b) give reasons for non-participation at each stage; and (c) “consider use of a flow diagram.” Consider a diagram when it makes participant numbers clearer, and check your target journal’s author instructions, as some journals ask for one.
My study has two periods of follow-up — how do I handle this?
Combine the follow-up losses from both periods into the single Follow-Up stage, and note the periods in your Methods section. If the losses differ substantially between periods, use the click-to-edit feature to add detail to the follow-up box label.
Should I combine reasons for exclusion?
List the main exclusion reasons individually in the exclusion box at the relevant stage. STROBE does not prescribe a maximum number of reasons — include the ones that account for the largest n and a catch-all “other” if needed. The reasons textarea format accepts one “Reason | n” entry per line.
Is there a STROBE extension for specific study designs?
Yes — STROBE has extensions for genetic association studies (STREGA), nutritional epidemiology (STROBE-NUT), and infectious disease modelling (STROME-ID), among others. The core participant flow structure is the same; the extensions add checklist items specific to the methodology. This tool implements the core STROBE flow diagram.

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References

  1. von Elm E, Altman DG, Egger M, et al. The Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) statement: guidelines for reporting observational studies. Lancet. 2007;370:1453–1457. PMID 18064739.
  2. Vandenbroucke JP, von Elm E, Altman DG, et al. Strengthening the Reporting of Observational Studies in Epidemiology (STROBE): explanation and elaboration. PLoS Med. 2007;4:e297. PMID 17941715.
  3. Elm E von, Altman DG, Egger M, et al. The Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) statement: guidelines for reporting observational studies. Ann Intern Med. 2007;147:573–577.

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