Testing two stage assessments in a Chinese college student sample: Correspondences and discontinuity patterns across stages

Objectives: Stage models are especially helpful when matching treatments to the needs of intervention participants. However, stage-matched treatments can only be effective if stages are assessed adequately. Therefore, the measurement qualities of the stage assessments need to be tested. The objective of the current study is to test two stage assessments, one measuring the stages of the Transtheoretical Model (TTM) and one measuring the stages of the Health Action Process Approach (HAPA). Design: Measurement qualities were tested by means of planned contrasts and higher-order trends (Study Purpose 1). The match of the two stage assessments were analyzed regarding their co-occurrence (Purpose 2). Also a " trimmed stage classification variable" was analyzed regarding its measurement qualities (Purpose 3). Method: A total of 830 Chinese college students received questions assessing social-cognitive variables as well as the HAPA- and TTM-stages. Discontinuity patterns were tested across the stages with planned comparisons and non-linear, higher-order trends. Results: TTM- and HAPA-stages corresponded with each other. However, a strong fit of the two stage assessments was not found and measurement error may be assumed. After trimming the stage assignments, the HAPA-assessment improved, and the TTM decreased in measurement qualities. Conclusions: After trimming the stage assignments and correcting for potential measurement error, a more parsimonious stage approach (i.e., HAPA) may be more appropriate.