Repeatability evaluation of a dairy farm management questionnaire

The purpose of the research reported in this paper was to examine the repeatability of a dairy farm management questionnaire. The questionnaire was used in a study of the effects of dairy farm management and bulk tank milk protein concentration (BTMPC). The repeatability was studied by a simple test-retest design and was incorporated into the overall design of the management-bulk tank milk protein project. The source population was farms in a specific region of the Netherlands that delivered milk without interruption from February 1987 onward, and had annual milk quotas of at least 250 000 kg. Repeatabilities of categoricaly scaled questionnaire items were estimated by the intraclass kappa coefficient. Repeatabilities of continuous-scaled items were estimated by Pearson's intraclass correlation coefficient. The standard error of each coefficient was estimated via a jackknife procedure. Influence of the following factors on question repeatability was examined: method of questionnaire administration, type of question, category of dairy farm management, and stratum from which the farms were sampled. The study also investigated the effect of dichotomization of polytomous response data on repeatability. Seventy-one percent of the questionnaire items ultimately introduced into the crude analysis of the farm management-BTMPC study had chance-corrected repeatability coefficients greater than or equal to 0.40. Sixty-nine percent of the items had coefficients greater than or equal to 0.50. Repeatability quality of the questionnaire was judged to be adequate and recommendations are made for dairy farm management questionnaire formulation.