How are the self-determination theory and the theory of planned behavior related?

Two psychological theories that you may have read about on this site are the self-determination theory and the theory of planned behavior. A new study (Chan et al., 2020) maps the relationships between these two theories.

The Self-Determination Theory

The self-determination theory (SDT) is now the most influential and best-researched motivation theory. The theory was originally developed by Richard Ryan and Ed Deci and is now being researched and further developed by a large network of researchers from around the world. 

An important concept from SDT is autonomous motivation. When we are autonomously motivated, we endorse what we are doing because we find the activity interesting or important. Autonomous motivation is associated with well-being and performance.

The Theory of planned behavior

The theory of planned behavior (TPB) was formulated by Icek Ajzen (1985) as a derivative of the theory of reasoned action (TRA). The theory focused on the question of how intentions to behavior come about. Three factors were considered important determinants of behavioral intentions: attitudes, subjective norms and perceived control over behavior. 

Important social cognitive concepts from TPB are: attitude (attitude), subjective norm (subjective norm) and perceived behavioral control. TPB assumes that individuals have the intention to perform goal-directed behavior when they have a positive attitude towards that behavior, the behavior is expected and seen as normal in their environment (subjective norm), and they feel they are able to do the behavior (perceived behavioral control).

How are SDT and TPB related to each other?

Chan et al. investigated how SDT and TPB are related. To do this, they conducted a longitudinal study, with measurement moments at three times, among physical education students in China. The students completed self-report questionnaires measuring autonomic motivation, attitude, subjective norm and perceived behavioral control with regard to sports injury prevention. They did this at a start time (T1) and at two follow-up moments: T2 (after 1 month) and T3 (after 3 months).

Findings

What can be seen in this table is that autonomic motivation (from SDT) predicted the constructs from TPB with small to medium effect sizes. There was hardly any reciprocal relationship. TPB constructs (attitude, subjective norm and PBC) hardly or not predicted autonomous motivation.

Conclusion

This research therefore seems to indicate that autonomous motivation from SDT is an antecedent of the constructs from TPB. Providing autonomy support could thus be a good way to make individuals' attitudes about the requested behavior more positive, to make them more aware that the behavior is normal and expected and that they are able to display the behavior .

Autonomy support can be given by taking the student's perspective seriously, offering them options, encouraging their own initiative and experimentation, involving them in decisions where possible and giving them a clear rationale for any requests.