Kullberg 1993.

Study characteristics
Methods	Study design: retrospective cohort longitudinal Location: Sweden Time period: 01 August 1988 to 31 October 1991 Outcome: PDR Outcome measurement: incidence and means of progressors versus non‐progressors to PDR
Participants	Number of participants: 172 Diabetes type: T1D Inclusion criteria: all T1D patients attending the diabetic outpatient clinic at the University Hospital, Linkoping during the period 01 August 1988 to 31 October 1991, with age at diagnosis of less than 31 years, diabetes duration 25 years or less, and with glycated haemoglobin measured for at least 5 years at the hospital, in the absence of or before the appearance of PDR or nephropathy Exclusion criteria: not explicitly stated as criteria, but excluded those with multiple endocrine insufficiency and hypothyroidism with impaired renal function, abnormal haemoglobin, and pregnancy
Notes	Link to data extraction table, risk of bias assessment, and results: osf.io/fkmzr/?view_only=7fbd4103b88d4f9d8cf7c5c8e34a91e8
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	Yes	See ‘Notes’ above for link to risk of bias assessment
Adjustment for other prognostic factors	Unclear	See ‘Notes’ above for link to risk of bias assessment
Statistical analysis and reporting	Unclear	See ‘Notes’ above for link to risk of bias assessment