Psychometric properties of the revised Diabetes Knowledge Test using Rasch analysis

•The revised Diabetes Knowledge Test (DKT2) is the most frequently used instrument.•The first test of structural validity of the DKT2 yielded unidimensionality.•It is necessary to improve the poor internal consistency of the DKT2.•It is necessary to add new items of greater difficulty to the DKT2. The revised Diabetes Knowledge Test (DKT2) is the instrument that is the most widely used for measuring diabetes knowledge; nevertheless, its structural validity has never been evaluated. This study aimed to determine the psychometric properties of the DKT2. This study performed a secondary data analysis of people with diabetes recruited at university hospitals. Rasch analysis was used. One item in the 14-item DKT2 measuring general diabetes knowledge exhibited a poor-fit, and so it was eliminated. The person-item map showed that items of greater difficulty need to be added to the instrument. The principal-components analysis of residuals revealed a unidimensional structure. The person reliability was 0.50, with a person separation index of 1.01. Measurement invariance was not satisfied for items 11 and 2 according to gender and age. The unidimensional structure of the 13-item DKT2 demonstrated poor person reliability and a low person separation index. Females and elderly persons found it more difficult to respond to items 11 and 2, respectively. Careful consideration is necessary when using the 13-item DKT2 in practice and research. It is recommended for future studies to add items of greater difficulty to the instrument.