Further evidence that only children are not more narcissistic than individuals with siblings

Are only children more narcissistic than individuals with siblings? Prior research on the topic has produced conflicting and/or inconclusive results. Dufner et al., 2019 published a recent and widely reported empirical test of this hypothesis and concluded that only children are not more narcissistic than non-only children. One of their acknowledged limitations was that their study was limited to the German population. They called for additional tests in other countries. In this paper, we report results from a high-powered test of this hypothesis using multiple measures of narcissism (i.e., two full-scale and 10 facet-level measures) and a large sample (N = 8,689) of American college students. Despite this study possessing extraordinary statistical power, we likewise fail to observe any notable differences in narcissism between only children and non-only children. Follow up equivalence and Bayesian testing suggested generally strong to very strong support for the null hypothesis that only children and non-only children are equivalent in terms of narcissism.