Development and validation of a scale to measure patients' trust in pharmacists in Singapore

To develop and validate a scale to measure patients' trust in pharmacists for use as an outcomes predictor in pharmacoeconomic and pharmaceutical care studies.

Literature review, study team discussion and focus group discussions were conducted to generate items of a candidate version to be pilot-tested for content validity. An amended candidate version was then tested among eligible Singaporeans across different ethnic and age groups. Score distributions were assessed for discriminatory power and item analyses for finalizing items. Exploratory factor analysis was used to identify dimensionality and homogeneous items. Cronbach's alpha was measured for internal consistency and Pearson's correlation coefficients for convergent validity.

Eighteen items were generated with good variability (SD > 1.0) and symmetry (means ranged from -1 to 1) for score distribution. After minor changes to improve content clarity, the amended questionnaire was self-administered among 1196 respondents [mean (SD) age: 38.6 (14.9) years, 51.6% female, 87% >6 years of education]. Six items were dropped due to inadequate item-total correlation coefficients, leaving 12-item scale for factor analysis. Three factors ("benevolence", "technical competence" and "global trust") were identified, accounting for 55% of the total variance. Cronbach's alpha was 0.83, indicating high internal consistency. Convergent validity was demonstrated by statistically significant positive correlations between trust and patients' satisfaction with pharmacists' service (r = 0.54), returning for care (r = 0.30) and preference of medical decision-making pattern (r = 0.16).

The 12-item trust in pharmacists scale demonstrated high reliability and convergent validity. Further studies among other populations are suggested to confirm the robustness and even improve the current scale.