The purpose of this study is to review the concepts used for the expansion of the theory of planned
behavior and to show the change of variance of additional variables of the theory of planned behavior.
To do this, this study examined how much the addition of these concepts contributed to the increase
in the explanatory power of the theory of planned behavior. Through a meta-analysis on 217 studies
published up to the end of 2016 in Korea. The most frequently used concepts in the extension of the
theory of planned behavior are past behavior, habit, past experience, moral norm, group norm,
descriptive norm, knowledge, self-efficacy, self-identity, and implementation intention. The habit,
past behavior, and moral norm had a great effect to increase variance explaining the behavior intention
or behavior. Also this study has found that these concepts could be useful to extend the theory of
planned behavior. This finding implies that additional variables are significant in the extension of the
theory of planned behavior. Based on the findings of the present meta-analysis, this study discussed
the future directions in which current the theory of planned behavior research can be taken forward.