Below is a short summary of a new study I published in the Journal of Psychosomatic Research. In this study, I investigated several methods used to assess a Type D personality effect and showed that the commonly used methods based on personality subgroups may result in false positive Type D effects.
Modeling synergy: How to assess a Type D personality effect
In research on Type D personality, its subcomponents negative affectivity (NA) and social inhibition (SI) are hypothesized to have a synergistic effect on various medical and psychosocial outcomes. As some methods to analyze Type D personality have been criticized, this study investigated whether these methods adequately detect a Type D effect. We used a simulation and two empirical illustrations to investigate each method’s performance (bias, power and false positives) in detecting the Type D effect. Our simulation showed that the two most commonly used methods to assess the Type D effect (subgroup methods) were primarily picking up the presence of NA or SI main effects, indicating that these methods might falsely suggest synergistic Type D effects. Moreover, these methods failed to detect the combined presence of the NA and SI main effects, resulting in significant Type D effects when only one of the NA/SI main effects was present. The method that best detected Type D effects modeled the continuous NA/SI main effects and their statistical interaction in a regression analysis. Reanalysis of two empirical Type D personality datasets confirmed the patterns found in our simulation. This study showed that Type D effects should be modeled with a continuous interaction approach. Other approaches showed either more bias, more false positive findings or lower power. We recommend against using subgroup approaches to operationalize Type D personality, as these methods are biased, regardless of whether the Type D effect is synergistic or additive in nature.
Lodder, P. (2020). Modeling synergy: How to assess a Type D personality effect. Journal of Psychosomatic Research, 109990.