Better find a new go-to argument, siblings: Your birth order doesn't actually mean all that much. A new study from the University of Illinois found that the effect birth order has on personality traits and intelligence is negligible, at best. Reported in the Journal of Research in Personality, the study notes that first-born children do have an extra IQ point and slightly more extroverted personalities, but that the differences are "infinitesimally small.” "If a drug saves 10 out of 10,000 lives, small effects can be profound," University of Illinois professor Brent Roberts said.