Spaulding 1991

Methods	Purpose: to compare a postcard reminder sent to high‐risk participants on influenza immunisation uptake to usual care (no postcard) Design: RCT Duration of study: 6 months Time: 1983/1984 influenza season Outcome measured: % vaccinated against influenza for the 1983 to 1984 season by sex, rank of military sponsor and age group (including those aged > 64 years) Interval between intervention and when outcome was measured: 6 months were allowed for people to be vaccinated and it is clear that the intervention ante‐dated the measurement of outcome Power computation: no information provided Statistics: Chi2 statistic to compare proportions vaccinated each group. Multivariate analysis using Mantel‐Haenszel (M‐H) Chi2 statistic and M‐H adjusted risk ratio. Within‐family clustering was not addressed
Participants	Country: USA Setting: Department of Family practice at Madigan Army Medical Center, Ft Lewis Washington Eligible participants: 1068 military retirees or the family members of active or retired members of the military who had one or more high‐risk diagnoses for influenza complications according to the US Immunization Practices Advisory Committee criteria of 1983 Age: persons of all ages 0 to 20 years: 153 (71 intervention group 1; 82 control) 21 to 40 years: 130 (63 intervention group 1; 70 control) 41 to 64 years: 289 (269 intervention group 1; 289 control) 65  years or older: 224 (116 intervention group 1; 108 control) Sex: males 56.3%, females 43.7% Males: 573 (519 intervention group 1; 549 control) Females: 496 (257 intervention group 1; 238 control) Exclusions: persons who did not have high‐risk health conditions
Interventions	Intervention 1: 519 participants in intervention group were mailed a reminder postcard advising them that their physician had determined that they were at high risk of complications should they catch the flu and strongly urging them to come to the Family Practice Clinic for intervention. Postcard sent 2 weeks before availability of the influenza vaccine used during the 1983/84 season Control: 549 participants who received routine care, were not sent a postcard
Outcomes	Outcome measured: % receiving influenza vaccine based on office records of being vaccinated Time points from the study that are considered in the review or measured or reported in the study: from time postcard sent 2 weeks before vaccine availability to 6 months after vaccine became available Intervention: postcard sent 2 weeks before availability of the influenza vaccine used during the 1983/84 season % vaccinated by 6 months after the influenza vaccine used in the 1983/1984 season became available
Notes	Potential participants were assigned a code number that included 2 digits to identify if they were members of the same family. These data were not used in analysis (i.e. within‐family clustering was not addressed in the data analysis) There was no cost to patient for influenza immunisation No data are provided on influenza vaccination prior year Funding: no information provided
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Individuals were assigned to intervention or control group by a table of random numbers
Allocation concealment (selection bias)	Unclear risk	No information provided
Blinding (performance bias and detection bias) All outcomes	High risk	Physicians in the Department of Family Practice were aware that a study was in progress and that some of their participants might receive postcards about influenza immunisation. Vaccine was offered to all eligible participants on a walk‐in basis. Patients who presented for immunisation read and signed an informed consent document It is not stated if the physicians were those who performed the vaccinations. However, it is likely that participants might have told their vaccinator whether or not they had received a postcard
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	No information provided on attrition or incomplete data points. No analysis whether differential attrition could affect results; vaccination status assessed from records at US Army Medical Centre
Selective reporting (reporting bias)	Low risk	No selective reporting

avg: average CDC: Centers for Disease Control and Prevention CI: confidence interval COPD: chronic obstructive pulmonary disease C‐RCT: cluster‐randomised controlled trial dx: diagnosis f: female GI: gastrointestinal GLE ANOVA: general linear model repeated‐measures analysis of variance GPs: general practitioners HMO: health maintenance organisation ICD‐9‐CM: International Classification of Diseases 9th Revision Clinical Modification IHD: ischaemic heart disease ITT: intention‐to‐treat n: number ns: non‐significant OR: odds ratio RCT: randomised controlled trial RR: risk ratio SD: standard deviation