Assessing Nonresponse Bias in Farm Injury Surveillance Data.

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Despite a response rate of about 18%, there was scant evidence of nonresponse bias. Farm and ranch characteristics of operations responding to a mailed survey were similar to those not responding. Responders were significantly more likely to be married but only slightly older and more educated than nonresponders. Earlier survey responders reported more injuries and greater severity when injured compared to later responders. Nonresponse bias in a survey can result in misleading estimates of agricultural injuries and can misdirect prevention efforts aimed at reducing the burden of injuries on farmers. Responders (n = 2,977) and nonresponders (n = 13,849) were compared based on demographics and agricultural production characteristics to identify underrepresented subgroups. Injury characteristics were compared between early (n = 1,667) and late (n = 1,309) responders. Methods accounted for correlated data, sample size inflation of p-values, and assessment of meaningful differences. Few differences were identified between responders and nonresponders. Responders differed from nonresponders by state of residence, and responders were more likely to be married. Other characteristics (age, gender, education, farm size, crops grown, animals raised) were similar across groups. Early responders reported more injuries and more often sought medical care for an injury than late responders. The differences identified between responders and nonresponders were minimal and not likely to create bias. Differential reporting of injury and injury severity between early and late responders is worthy of further investigation.