RESEARCH_FILE
The Science of Family Favoritism
Most parents insist they love their children 'the same.'
SEE THE PRACTICE
Turn a thought this research explains into one clear move.
THE THOUGHT
“I'll never be the favorite in this family”
YOUR RECORDED RESPONSE
“The ranking is their accounting error, not my worth.”
ONE PRIVATE MOVE
Take a blank note and make three columns: noticed, assumed meaning, and another explanation. Fill in just one family memory from the past week, then fold the note and put it away.
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
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. ↗
What people believe vs. what the data shows
The belief“If parents say they don't have a favorite, they don't.”
The dataIn interviews, about 70% of mothers privately named a child they felt closest to, even though public denial of favoritism is the social norm. Suitor and Pillemer note mothers were visibly reluctant to admit it — reluctance to say it out loud isn't evidence it isn't happening. ↗
The belief“You always know who your parent's favorite is — you've felt it your whole life.”
The dataAdult children were fairly accurate about whether their mother favored someone, but far less accurate about which sibling it was, and the children who weren't the favorite were often the most confident that they were — a documented gap between perception and reality, not a reliable sixth sense. ↗
The belief“Birth order determines your personality — firstborns are natural leaders, the youngest is always the rebel.”
The dataThe largest test of the claim, drawing on more than 20,000 people across three countries, found no meaningful effect of birth order on any of the Big Five personality traits. Whatever differences siblings develop, raw birth position isn't the mechanism driving them. ↗
The belief“Only the child who wasn't favored gets hurt by favoritism — the favorite comes out fine.”
The dataPerceived maternal differential treatment predicted more depressive symptoms in midlife for the favored and the unfavored child alike. The favored child often carries added pressure, guilt, and strained sibling relationships rather than escaping the effects. ↗
The belief“Siblings who turned out completely different just have different natures — favoritism has nothing to do with it.”
The dataSibling deidentification research shows siblings, especially those close in age, actively exaggerate their differences from one another as a strategy to reduce rivalry and comparison. Family dynamics, including who a parent singles out, help shape those 'opposite' identities rather than sitting outside them. ↗
TEST_YOURSELF · How well do you know this science?
01 In interviews with Boston-area mothers, roughly what share privately named a child they felt closest to?
About 70% of the 275 mothers interviewed named a specific child they felt closest to, even though publicly denying favoritism is the social norm and most were reluctant to say so outright. source ↗
02 According to 'I'm Sure She Chose Me!' (Suitor et al., 2006), how accurate were adult children at naming which sibling their mother actually favored?
Children were fairly accurate about whether their mother favored someone at all, but only about 39% correctly named which sibling — and children who weren't chosen were often the most sure they were. source ↗
03 What does sibling deidentification theory (Schachter et al., 1976) propose?
Schachter and colleagues found deidentification was most pronounced between siblings close in age, who adopt distinct interests, traits and roles as a strategy to reduce rivalry and comparison — differences that are partly made, not just born. source ↗
04 What did the largest study of birth order and personality (Rohrer, Egloff & Schmukle, 2015) conclude?
Across more than 20,000 people in Germany, the US and Britain, birth order had no meaningful effect on extraversion, emotional stability, agreeableness, conscientiousness or imagination — undercutting the popular claim that birth position drives personality. source ↗
05 Whose wellbeing did perceived maternal differential treatment affect, according to the 2010 Journal of Marriage and Family study?
Pillemer, Suitor and colleagues found perceived differential treatment predicted more depressive symptoms in midlife for both the favored and the unfavored sibling — favoritism carries costs even for the child who benefits from it. source ↗