Methods to develop and evaluate attitudinal scales to measure farmer perceptions: Using sheep scab as an example

There is limited information on the attitudes and opinions of British sheep farmers when preventing and managing sheep scab in their flocks. Attitudes are examples of latent traits, which are not directly observable. They must be measured indirectly which can be achieved using measurement scales. Attitudinal measurement scales are used frequently in research, but are seldom evaluated prior to use, particularly in veterinary research. Therefore, the aim of this study was to identify and assess latent traits which influence the control of sheep scab with the use of exploratory factor analysis, and then further evaluate these factors with the use of item response theory to determine how they perform as scales. An online survey was completed by 726 British sheep farmers during October 2021 (725 useable responses), which included a section with 37 belief statements related to the opinions and attitudes of sheep farmers around the management of sheep scab. These belief statements were developed and adapted from previous research. During the analysis, they were subjected to exploratory factor analysis, which suggested that the scales performed reasonably well. The scales were then evaluated further by item response theory. The graded response models for each attitudinal scale were assessed by graphical evaluation. They demonstrated that the scales were able to distinguish those respondents with low perceptions of control, responsibility, and trust, and those who had high perceptions of luck. This study provides insights into some of the factors influencing the management of sheep scab, and how well these scales perform. Additionally, it further highlights the importance of evaluating attitudinal scales for use in research, and that exploratory factor analysis alone does not provide enough information on how well they perform.