Porta 2001.

Study characteristics
Methods	Study design: prospective cohort longitudinal Location: Europe Time period: baseline data 1989 to 1991 Outcome: PDR Outcome measurement: incidence, mean, median and percentage difference, OR, and standardised regression estimates
Participants	Number of participants: 3250 Diabetes type: T1D Inclusion criteria: diagnosed T1D < 36 years; insulin within 1 year of onset; age 15 to 60 years Exclusion criteria: centre drop‐out; no retinal photo at baseline or at follow‐up; PDR at baseline
Notes	Link to data extraction table, risk of bias assessment, and results: osf.io/hrp89/?view_only=96d5233896414d3a928a28b4e71441d7
Item	Authors' judgement	Support for judgement
Study participation	Unclear	See ‘Notes’ above for link to risk of bias assessment
Study attrition	Unclear	See ‘Notes’ above for link to risk of bias assessment
Prognostic factor measurement	Yes	See ‘Notes’ above for link to risk of bias assessment
Outcome measurement	Yes	See ‘Notes’ above for link to risk of bias assessment
Adjustment for other prognostic factors	Yes	See ‘Notes’ above for link to risk of bias assessment
Statistical analysis and reporting	Yes	See ‘Notes’ above for link to risk of bias assessment