Revisiting the relationship between birth order and romantic jealousy: No support for an effect in four samples

Birth order has long been argued to be an important individual difference variable for domains such as personality and achievement. However, after many decades of research, the evidence for a birth order effect is scarce at best. Less is known about the role of birth order for social relationships, in particular romantic relationships. This paper re-examines a previously reported finding that firstborns report less romantic jealousy than laterborns. We present data from four samples (total n > 950) with a MANOVA design, mirroring the study on which this original claim was based. Across all samples and multiple robustness checks, we found no statistical support for the claim that firstborns report less jealousy than laterborns. Both frequentist and Bayesian meta-analyses did not support a birth order effect on jealousy (frequentist estimate: r = 0.08, 95% CI [−0.018, 0.170]). These findings challenge the notion of birth order as a significant predictor for romantic jealousy and suggest that research on romantic relationships may yield greater insight by focussing on other individual difference variables than birth order.