Pirart 1977.

Study characteristics
Methods	Study design: prospective cohort longitudinal Location: Belgium Time period: 1947 to 1973 Outcome: PDR Outcome measurement: incidence, mean, median and percentage difference, OR, and standardised regression estimates
Participants	Number of participants: 3250 Diabetes type: not reported Inclusion criteria: proven diabetes for 2 to 25 years – documented hyperglycaemia found on several occasions of true blood sugar above 140 mg per decilitre either fasting or at least 2 hours after ingestion of 50 g of glucose, fasting; consulted for a complication of or instability of diabetes; both retinas visible Exclusion criteria: diabetes duration of more than 25 years
Notes	Link to data extraction table, risk of bias assessment, and results: osf.io/zuqfa/?view_only=7d8d92459e3f45f8ac13d00717b7b263
Item	Authors' judgement	Support for judgement
Study participation	Unclear	See ‘Notes’ above for link to risk of bias assessment
Study attrition	No	See ‘Notes’ above for link to risk of bias assessment
Prognostic factor measurement	Unclear	See ‘Notes’ above for link to risk of bias assessment
Outcome measurement	Unclear	See ‘Notes’ above for link to risk of bias assessment
Adjustment for other prognostic factors	No	See ‘Notes’ above for link to risk of bias assessment
Statistical analysis and reporting	No	See ‘Notes’ above for link to risk of bias assessment