SCIENCE / MEDICINE : The Myth of Birth Order : Is the oldest the smartest? Is the middle child the peacemaker? Those are popular beliefs, but most researchers say it’s just bunk.

There are people who maintain that just from knowing whether someone is a first-, middle- or last-born child, they can predict that individual’s personality and intelligence.

But then there are also people who take horoscopes seriously.

“Birth order really doesn’t explain a whole lot,” said Toni Falbo, an educational psychologist at the University of Texas at Austin, who has been studying the subject for 15 years. “But people like it. It’s much like astrology. It says, ‘I’m not to blame for the way I am.’ ”

For many years, the significance of one’s position in the family seemed--unlike astrology--to be supported by hard data. Studies purportedly showed that eldest children were more likely to be high achievers, and the babies of the family grew up to be unusually sociable.

But most of this research has been largely discredited. Although one recent, impressive study, still unpublished, does suggest that later-borns are more rebellious, the rule of thumb is that the better, the later and the larger the study, the less likely it is to find that birth order is a useful predictor of anything.

In fact, when Swiss social scientists Cecile Ernst and Jules Angst reviewed about 1,500 studies in 1983, they concluded that further research in the area would be a waste of money.

Popular periodicals continue to make much of birth order, sometimes offering meaningless generalizations such as: Middle children are usually peacemakers--or else they are competitive. Recently, an article in a women’s magazine claimed that Jane Fonda and Tom Hayden’s happy marriage was predictable on the basis of their respective birth orders. (The two split up just after the article went to press.)

Academics traditionally have been no less enamored of the idea. Birth order is easy to measure, and the idea that it tells us something about an individual is intuitively plausible.

But some specialists noticed that theories could be invented to account for whatever contradictory results were obtained. For decades, according to Judith Blake, a demographer at UCLA, publications on the subject have been characterized by an “unexpected ‘discovery’ of some birth-order difference and then an ad hoc effort to explain it.”

Blake is the author of Family Size and Achievement, a recent review of data on 150,000 individuals. She concludes that “once you control for family background factors, birth order doesn’t make any difference” with respect to either cognitive ability or number of years spent in school.

On the other hand, as the title of her book suggests, the number of siblings does matter. “Small families are, on average, much more productive of the kind of intellectual ability that helps people succeed in school,” she said in an interview. The reason is that both financial resources and attention are diluted in larger families.

Blake’s book contains a detailed rebuttal to the “confluence theory” offered by University of Michigan psychologist Robert Zajonc in the mid-1970s. Zajonc made headlines with his claims that standardized test scores can be predicted by the number of first-borns, second-borns, etc. taking the test.

Michael Berbaum, a research scientist at the University of Alabama, was a student of Zajonc and remains a defender of confluence theory. Yet he concedes that “there’s very little birth order effect in whatever standardized tests measure. Maybe eldest kids have five more IQ points on average, but five IQ points won’t buy you much in real life.”

Blake and others doubt that eldest children can claim even those few extra points when compared to other children in the same size families. Blake, for example, looked at birth patterns before 1938 and compared them to SAT scores for that group of children--just as Zajonc had done for a later period. There was no connection.

It seems more likely that birth order would help determine one’s personality. The psychoanalyst Alfred Adler argued in the 1920s that the first-born never recovers from being “dethroned” by the arrival of a brother or sister. Some clinicians still think that self-esteem, empathy, popularity and other traits are affected by birth order in consistent ways.

But controlled studies don’t bear this out. Ernst and Angst concluded that “birth order differences in personality . . . are non-existent in our sample. In particular, there is no evidence for a ‘first-born personality.’ ”

Nowhere are the myths more pervasive than in the case of only children, who, according to surveys, are widely perceived as being self-centered, unhappy and spoiled. Is there any truth to this profile?

None whatsoever, Falbo said. She and a colleague reviewed 141 studies in 1987 and found that “only children are not substantially different from other children who are raised with siblings with respect to personality characteristics.” Where small differences were found--such as in achievement motivation--they invariably favored the “onlies.”

One exception to this overwhelming failure to find birth order differences is a new and still unpublished study by Frank Sulloway, a historian of science who is a visiting scholar at Massachusetts Institute of Technology.

Sulloway’s exhaustive review of scientific controversies over the centuries shows that later-borns are more likely to support radical new ideas while first-borns oppose them. The reason, he suggests, is that “first-borns tend to identify more closely with parents and, through them, with other representatives of authority (while later-borns) rebel against the authority of their elder siblings.”

Birth order, Sulloway said, is a more accurate predictor of one’s position on a controversial new idea than social class, age, religion or anything else he examined. Thus, of Darwin’s contemporaries, three-fifths of later-borns supported the idea of natural selection, while only one-fifth of first-borns did.

“The only area where you expect pay dirt in birth order studies is conformity and attitudes toward authority,” Sulloway explained in an interview. “The reason I’m getting great data is that I picked the one thing birth order is relevant to.”

Until Sulloway’s paper is reviewed and accepted by others in the field, though, the conclusion seems unavoidable that birth order by itself tells us little or nothing about someone’s skills or character.

This is true, specialists say, because one’s position in the family means little apart from the norms of that family--whether sibling rivalry was promoted or discouraged, for example--and the norms of the culture.

“It makes a difference whether a culture places an emphasis on primogeniture or the rights of first-borns in general,” Berbaum said. A child being groomed to take over the family business, for instance, would probably receive more attention and encouragement, and those parental practices (rather than birth order itself) could well affect how a child develops.

In fact, adds Linda Musun Baskett, a psychologist at the University of Arkansas, the very belief in birth order stereotypes may lead parents to treat their children differently, “thus creating a self-fulfilling prophecy.”

But any effects on children’s cognitive skills and personality will probably be washed out by all the other influences in a person’s life. The belief in the lifelong impact of birth order, according to Falbo, is just one more example of “a holdover in our psychological theorizing--that your personality is fixed by the time you’re 6. That assumption is simply incorrect.”

Most of the early studies that seemed to show an effect were plagued by various methodological problems. The most common error is failing to tease apart the effects of family size and social class. If eldest children seemed to be overrepresented among high achievers, for example, it was probably because a disproportionate number of children from small families are present in any group of first-borns. (Every family has one first-born; fewer have a fourth-born.)

Moreover, when fertility rates fluctuate, the relative number of first-borns does too. Some studies of people born just after World War II didn’t take the Baby Boom into account.

What, then, of the commonly held assumptions about the impact of birth order? Said Blake: “They’re not worth anything. That’s the size of it.”

But, she adds, “You’re never going to completely put to rest what people think is fun to believe about these things.”