An evaluation of the psychometric properties of the Purdue Pharmacist Directive Guidance Scale using SPSS and R software packages

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Abstract

Background:

The Purdue Pharmacist Directive Guidance (PPDG) Scale was developed to assess patients' perceptions of the level of pharmacist-provided (1) instruction and (2) feedback and goal-setting—2 aspects of pharmaceutical care. Calculations of its psychometric properties stemming from SPSS and R were similar, but distinct differences were apparent.

Objective:

Using SPSS and R software packages, researchers aimed to examine the construct validity of the PPDG using a higher order factoring procedure; in tandem, McDonald's omega and Cronbach's alpha were calculated as means of reliability analyses.

Methods:

Ninety-nine patients with either type I or type II diabetes, aged 18 years or older, able to read and write English, and who could provide written-informed consent participated in the study. Data were collected in 8 community pharmacies in New Mexico. Using R, (1) a principal axis factor analysis with promax (oblique) rotation was conducted, (2) a Schmid-Leiman transformation was attained, and (3) McDonald's omega and Cronbach's alpha were computed. Using SPSS, subscale findings were validated by conducting a principal axis factor analysis with promax rotation; strict parallels and Cronbach's alpha reliabilities were calculated.

Results:

McDonald's omega and Cronbach's alpha were robust, with coefficients greater than 0.90; principal axis factor analysis with promax rotation revealed construct similarities with an overall general factor emerging from R.

Conclusions:

Further subjecting the PPDG to rigorous psychometric testing revealed stronger quantitative support of the overall general factor of directive guidance and subscales of instruction and feedback and goal-setting.

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