Subar 2001.

Study characteristics
Methods	Parallel RCT, individuals randomised
Data	USA, secondary care setting. Three out of 10 screening centres were included in this trial. Total n = 900; age of participants >50 years old, 51% were females.
Comparisons	Intervention group 1 received by mail the Diet History Questionnaire (including frequency of intake for 114 individual food items, five questions about the proportions, four summary questions, and nine questions on the use of vitamin and mineral supplement) accompanied by a cover letter and a postage‐paid return envelope. Intervention group 2 received by mail a 36‐page machine readable food frequency questionnaire, accompanied by a cover letter and a postage‐paid return envelope. For participants who did not return their questionnaires within three weeks, up to five telephone calls were made by staff at each centre.
Outcomes	Questionnaires returned
Notes	Retention period: 36 months
Risk of bias
Item	Authors' judgement	Support for judgement
Allocation concealment?	Unclear	Not reported in the paper.
Adequate sequence generation?	Unclear	Not reported in the paper.
Blinding of participants and personnel?	Unclear	Not reported in the paper.
Blinding of outcome assessment?	Unclear	Not reported in the paper.
Incomplete outcome data addressed? All outcomes	Unclear	Not reported in the paper.
Free of selective outcome reporting?	Unclear	Not reported in the paper.
Other sources of bias	Unclear	No concerns raised.
Overall Risk of Bias	Unclear	Unclear