Constructing licensure exams: a reliability study of case-based questions on the National Board Dental Hygiene Examination.

Patient cases with associated questions are a method for increasing the clinical relevance of licensure exams. This study used generalizability theory to assess changes in score reliability when the number of questions per case varied in the National Board Dental Hygiene Examination (NBDHE). The experimental design maintained the same total number of case-based items, while varying the number of cases and items within cases to assess changes in score reliability. Using generalizability theory, the amounts of error variance within cases and between cases on the NBDHE were assessed. Impact on score reliability (generalizability) was computed. The data were from the responses of 4,528 candidates who took the paper-pencil version of the NBDHE in spring 2009. Results showed that the minimum value of generalizability occurred when fourteen cases with ten items each were used in the examination. The maximum value of generalizability occurred when fifty cases with three items each were used in the examination. The research findings support the development of more cases with fewer items per case on the NBDHE in order to enhance test score reliability and validity. Practical constraints should be considered if more cases with fewer items per case are developed for future examinations.