Development and validation of a scale to measure the quality of patient medication counseling using Rasch model

The purpose of this study is to develop and validate the psychometric properties of a scale for measuring the quality of patient medication counseling by using the Rasch model.

In this study, the scale was developed based on the literature review. It consisted of 31 items across five subscales: introduction, problem identification, content, behavior, and conclusion. A convenient sample of community pharmacists was recruited from four major cities in Vietnam: Hanoi, Da Nang, Ho Chi Minh, and Can Tho. Data collection was conducted from June 10 to October 30, 2017. A Rasch analysis for polytomous data was performed to assess the suitability of the item and the reliability of the scale.

The research results showed that all items had a positive point-measure correlation coefficient between 0.47 and 0.77. All items had infit and outfit values in the optimal range between 0.5 and 1.5 except for D₅, but its value was within acceptable range. Differential item function analysis indicated that all items had no DIF, except for items B₄ and E₄ containing moderate magnitude of DIF. Response category statistics found that there was a gradual increase in difficulty level from category 1 to 5 and no presence of reversal. Infit and outfit statistics of these categories were also considered good, with their values close to 1. The test result of the item characteristic curve and the person-item map showed that there were some overlapping items. Their appearance, however, might play an important role in measuring different aspects of construct. The overall scale reliability index (0.97) was high and the overall scale separation index (6.11) was good.

The developed scale satisfied the requirements of the Rasch model. The scale is a useful tool that could be used to measure the quality of patient medication counseling among community pharmacists.