McMahon 1995a

Methods	Purpose: to compare an individual letter plus an informational brochure about influenza vaccination to a form letter plus brochure to no intervention in Montana Design: RCT; Montana was divided into 24 geographic regions and Wyoming into 16 by zip codes and 4 regions randomly assigned from each to intervention Duration of study: 3 months Interval between intervention and when outcome was measured: brochure or letter mailed 23 to 30 September 1994; vaccination uptake assessed 1 to 31 December 1993 and 1994   Power computation: not performed Statistics: logistic regression to examine relationship of letter plus brochure and influenza vaccination; Egret® statistical software to adjust for confounding variables
Participants	Total number: Montana: personalised letter 19,850, form letter 21,250, no letter 150,000; Wyoming same numbers Setting: all Medicare beneficiaries in Montana and Wyoming Diagnostic criteria: % receiving influenza vaccination recorded as influenza vaccination claims submitted to HCFA (Medicare pays for influenza vaccination for all those enrolled in Medicare Part B, and 96% of those ≥ 65 in the US are enrolled in Medicare Part B) Gender: not stated Age: ≥ 65 Country: USA [Co‐morbidity not stated] [Socio‐demographics not stated] [Ethnicity not stated ] [Date of study 1994]
Interventions	Intervention 1: individual letter plus an informational brochure about influenza vaccination Intervention 2: form letter plus brochure Control: no intervention [Integrity of Intervention not stated]
Outcomes	Outcome measured: % vaccinated Time points from the study that are considered in the review or measured or reported in the study: intervention in September, influenza vaccination claims October 1 through 31 December 1993 and 1994 % vaccinated by: 31 December 1985 Note: n's in McMahon 1995a and McMahon 1995b differ from those in Maglione 2002a. We adopted the n's in Maglione 2002a because the authors reported extracting data independently in duplicate, comparing them and resolving discrepancies
Notes	Funding: Montana‐Wyoming Foundation for Medical Care
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	"The two states were divided into 40 geographic regions defined by zip code aggregates (24 in Montana, 16 in Wyoming); in each state four regions were randomly selected as intervention sites."
Allocation concealment (selection bias)	Unclear risk	No statement
Blinding (performance bias and detection bias) All outcomes	Unclear risk	No statement
Incomplete outcome data (attrition bias) All outcomes	Low risk	Influenza vaccination data are collected by Medicare as billing claims
Selective reporting (reporting bias)	Low risk	No selective reporting