Development of a Vaccine Advocacy Scale for Childhood Vaccines and Psychometric Evaluation: A Methodological Study

Aim: This study developed the Vaccine Advocacy Scale for childhood vaccines for adults and evaluated its psychometric properties. Method: This methodological study involved 211 adults. A literature review was conducted to create the item pool of the scale, and 12 items were prepared. While evaluating the scale's psychometric properties, the researchers performed content validity, explanatory factor analysis (factor loadings of the items, eigenvalues of the sub-dimensions, and explained variance rates), confirmatory factor analysis (factor loadings and common fit indices), and criterion validity (predictive validity) in the validation phase. In the predictive validity assessment, the distribution of scores on the scale was examined according to some behaviours related to vaccine advocacy. Additionally, we analysed the item-total score correlation, Cronbach's alpha coefficient, and split-half test consistency in the reliability phase. Results: The study's calculated Kaiser-Meyer-Olkin value was 0.868, and Bartlett's test of sphericity resulted in significant results (X2 = 1724.166; p < 0.001). The explanatory factor analysis revealed that the items' factor loadings were between 0.451 and 0.949 and explained 58.29% of the total variance of the structure, which consisted of 12 items and two sub-dimensions. The confirmatory factor analysis found the factor loadings of the items between 0.62 and 0.85 and identified 'common fit indices' within acceptable ranges and close to the perfect fit values (X2/df, GFI, CFI, RMSEA, RMR, NFI, TLI and IFI were 1.906, 0.950, 0.952, 0.093, 0.059, 0.906, 940 and 0.953, respectively). The Cronbach's alpha value for the scale was 0.92, and the Spearman-Brown coefficient, Guttman's split-half coefficient, and split-half correlation coefficients were 0.843, 0.842 and 0.713, respectively. The study findings indicated that individuals who had talked to other parents about vaccines, recommended vaccinations, and communicated vaccine-related issues with medical professionals had significantly higher total scale scores (p < 0.005). Conclusion: Considering the study findings and evaluations, the Vaccine Advocacy Scale was a valid and reliable measurement tool to assess adults' vaccine advocacy behaviour for childhood vaccines.