Comparing the findings of two popular methods used to estimate a Type D personality effect

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In this newly published study, me and my collaborators studied the differences between two methods that are commonly used in the literature to estimate a Type D personality effect. Type D personality, operationalised as high scores on negative affectivity (NA) and social inhibition (SI), has been associated with various medical and psychosocial outcomes. The recent failure to replicate several earlier findings could result from the various methods used to assess the Type D effect. Despite recommendations to analyse the continuous NA and SI scores, a popular approach groups people as having Type D personality or not. This method does not adequately detect a Type D effect as it is also sensitive to main effects of NA or SI only, suggesting the literature contains false positive Type D effects. Here, we systematically assess the extent of this problem. We conducted a systematic review including 44 published studies assessing a Type D effect with both a continuous and dichotomous operationalisation. The dichotomous method showed poor agreement with the continuous Type D effect. Of the 89 significant dichotomous method effects, 37 (41.6%) were Type D effects according to the continuous method. The remaining 52 (58.4%) are therefore likely not Type D effects based on the continuous method, as 42 (47.2%) were main effects of NA or SI only. Half of the published Type D effect according to the dichotomous method may be false positives, with only NA or SI driving the outcome. Our findings suggest that a large part of the Type D literature should be reanalysed to find out whether the results remain unchanged when using the continuous method.

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