Characteristic	No Imputation	Imputation
Eligible study population (all male respondents aged 45–79 y)	2,094	2,094
Nonrespondents to cardiovascular health module (no data on outcome, ie, aspirin use)	−1,163	0
Initial study population (respondents with data on aspirin use)	931	2,094
Exclusion criteria no. 1: contraindication to aspirin	−74	−163
Exclusion criteria no. 2: history of cardiovascular disease	−166	−367
Final study sample	691	1,564
At risk for myocardial infarctiona	518	1,182

^a The primary focus of the study was aspirin use among men at risk of myocardial infarction; therefore, most of the analyses were done on this subset of the study sample.