Motivation for PhD studies: Scale development and validation

• We developed and validated a scale for assessing motivation for PhD studies.
• Results from two samples supported a five-factor model with two higher-order factors.
• Correlations between subscales and various outcomes were in line with SDT.
• Complete measurement invariance was found across various subgroups of PhD students.

In Canada and the United States, doctoral attrition rates are estimated to vary from 40% to 60%. Motivation has been proposed as a determinant of doctoral degree completion. The purpose of this study was to develop and validate a scale based on self-determination theory, to assess five types of regulation (intrinsic, integrated, identified, introjected, and external) toward PhD studies. Based on two samples (N = 244, N = 1060), this study involved five steps: (1) item development, (2) factor validation, (3) reliability assessment, (4) convergent and discriminant validity assessment, and (5) measurement invariance testing. Findings from both samples were similar, supporting a five-factor first-order structure and a two-factor higher-order structure, scale reliability, and convergent and discriminant validity as shown by correlations among motivation subscales and correlations between each subscale and various outcomes. Additionally, complete measurement invariance was supported across gender, citizenship status, program type, age, and program progression.