Abstract

Most longitudinal, correlational studies on health-behaviour change examine
effects of Time1 social-cognitive predictors on subsequent behaviour. In contrast,
our research focusses on associations between changes in predictors with change
in behaviour. The Health Action Process Approach (HAPA) distinguishes
between motivational predictors for intention formation and volitional predictors
for behavioural change and served as theoretical basis. Two online-studies were
launched targeting different behaviours (low-fat diet, smoking), different samples
(Study 1: N¼469; Study 2: N¼441) and different time spans (Study 1: 3 months,
Study 2: 4 weeks). Data were analysed by means of structural equation modelling
with latent difference scores. Both studies resulted in almost parallel prediction
patterns. Change in risk awareness and change in outcome expectancies did not
result in change in intentions, whereas change in self-efficacy was of crucial
importance. Change in behaviour was associated with change in action planning
and action control over and above the effects of intentions. In one study,
increases in self-efficacy yielded increases in behaviour change. Results
demonstrate that change in action planning and especially action control was
of great importance for behaviour change across two different behaviours.
Analysing change in social-cognitive predictors allows drawing precise conclusions
for interventions.