Empirical similarity of responses of two random samples of North Carolina swine producers to a management questionnaire used in the US National Swine Survey

Abstract

The United States Department of Agriculture's (USDA) National Animal Health Monitoring System (NAHMS) National Swine Survey (NSS), implemented in 1990, represents the first national effort to collect on-farm data using a statistically valid method. The purpose of the North Carolina Swine Survey (NCSS) was to evaluate the reliability of the NSS by assessing the similarity of responses between the North Carolina portion of the NSS and the NCSS using identical questions. Responses from the North Carolina portion of the NSS ( n = 40 farms) and from the NCSS ( n = 139 farms) were compared for a subset of the first three questionnaires used in the NSS. Chi-square analysis was used to test for significant differences between estimated proportions from the two studies. Plots of component chi-square values and frequency distribution of differences between point estimates were used to evaluate the similarity between sections of the questionnaires. Approximately 75% of the 446 point estimates were within 15% of each other. The majority of significant discrepancies occurred for the biosecurity section of the second questionnaire, specifically for response categories of ‘No’ and ‘ N A ’ (not applicable). Percent of farms responding ‘Yes’ showed greater comparability between the two studies. While most questions from the first and third questionnaires (General Swine Farm Report and the Facilities and Feed Report) proved to be similar, questions regarding disease problems, vaccination and preventive practices were less similar between the two studies.