RESEARCH_TIMELINE
The Science of Family Favoritism: What the Research Actually Shows
Most parents insist they love their children 'the same.' Decades of research on parental differential treatment — led largely by sociologist Jill Suitor's long-running studies of Boston-area families — tell a more complicated story: most mothers privately do feel closer to one child, most are reluctant to admit it outright, and their adult children are often wrong about who it is. Meanwhile, the popular idea that birth order itself explains personality — the bossy firstborn, the rebellious baby of the family — has been tested across tens of thousands of people and mostly hasn't held up. What predicts adult wellbeing isn't your slot in the birth order, but whether you felt, or still feel, singled out. Here's how the science moved from folk theory to family surveys.
How the science changed · 1976–2015
- 1976
Frances Schachter and colleagues introduce sibling deidentification theory in Developmental Psychology: siblings, especially those close in age, actively exaggerate their differences from each other to reduce rivalry and comparison — meaning many 'opposite' siblings are less born different than made different. ↗
- 1996
Frank Sulloway's book Born to Rebel popularizes the claim that birth order itself shapes personality across the lifespan — firstborns as conventional and achievement-oriented, laterborns as rebellious risk-takers — reviving a century-old folk theory with new historical case studies. ↗
- 2006
Jill Suitor and colleagues publish 'I'm Sure She Chose Me!' in Family Relations, comparing mothers' and adult children's reports directly: children were fairly accurate about whether their mother favored anyone, but far less accurate about which sibling it was — and children who weren't the favorite were often the most confident they were. ↗
- 2007
In 'Mothers' Favoritism in Later Life,' Suitor and Karl Pillemer report that in interviews with 275 Boston-area mothers, about 70% named a specific child they felt closest to, 79% named a preferred future caregiver, and 73% named the child they argued with most — despite most mothers being visibly reluctant to admit favoring anyone. ↗
- 2008
Suitor, Sechrist, Plikuhn, Pardo and Pillemer synthesize the emerging 'within-family differences' framework in Current Directions in Psychological Science, arguing parental differential treatment (PDT) must be studied across the whole life course, not just childhood, since favoritism keeps shifting as parents and children age. ↗
- 2010
Pillemer, Suitor and colleagues report in the Journal of Marriage and Family that adult children who perceived their mother as favoring a sibling — or disfavoring themselves — showed more depressive symptoms in midlife, and that the effect held for the favored and unfavored child alike, not only the one left out. ↗
- 2015
Rohrer, Egloff and Schmukle publish the largest test of birth-order effects to date in PNAS, analyzing over 20,000 people across Germany, the US and Britain: birth order showed no meaningful effect on Big Five personality traits, directly undercutting the Sulloway-style narrative that birth position drives personality. ↗