Comparing solutions to the 'expectancy-value muddle' in the theory of planned behaviour

Objectives. The authors of the Theories of Reasoned Action (TRA) and Planned Behaviour (TPB) recommended a method for statistically analysing the relationship between the indirect belief-based measures and the direct measures of attitude, subjective norm, and perceived behavioural control (PBC). However, there is a growing awareness that this yields statistically uninterpretable results. This study's objective was to compare two solutions to what has been called the 'expectancy-value muddle'. These solutions were (i) optimal scoring of modal beliefs and (ii) individual beliefs without multiplicative composites. Design. Cross-sectional data were collected by telephone interview. Methods. Participants were 110 first-degree relatives (FDRs) of patients diagnosed with colorectal cancer (CRC), who were offered CRC screening in the study hospital (83% response rate). Participants were asked to rate the TPB constructs in relation to attending for CRC screening. Results. There was no significant difference in the correlation between behavioural beliefs and attitude for rescaled modal and individual beliefs. This was also the case for control beliefs and PBC. By contrast, there was a large correlation between rescaled modal normative beliefs and subjective norm, whereas individual normative beliefs did not correlate with subjective norm. Conclusions. Using individual beliefs without multiplicative composites allows for a fairly unproblematic interpretation of the relationship between the indirect and direct TPB constructs (French & Hankins, 2003). Therefore, it is recommended that future studies consider using individual measures of behavioural and control beliefs without multiplicative composites and examine a different way of measuring individual normative beliefs without multiplicative composites to that used in this study.