HOW do demographers get interested in their field? ``At the first opportunity I was given to do a survey,'' recalls Samuel H. Preston, chairman of the Graduate Group in Demography at the University of Pennsylvania, ``I did one.'' The place: his eighth-grade class at the public school in Yardley, Pa. The reason: A lower-than-expected grade in Latin.
``I was annoyed,'' Professor Preston recalled during an interview in his book-strewn corner office here. ``I felt this teacher was using standards that were inappropriate. So I surveyed everyone I could who had taken Latin from her, got their grades, and showed that the Latin grades were statistically significantly below the grades in other areas.
``I think that probably showed some predilection for numerical assessments of human groups,'' he chuckles. And that, he says, is what demography is all about. ``What fascinates me is the fact that human behavior in the aggregate is captured so accurately by our data systems in such important matters as marriage and divorce and fertility and mortality.''
For Preston, however, demography does not stop with the numbers. ``When you see a change or a difference among groups or countries in behavior, there has to be some explanation that drives you to other levels of interpretation.
``I think we're more interdisciplinary than any of the other social sciences, because we're not self-sufficient. We basically start with observations and then look for explanations.'' Those explanation are usually drawn, in fact, from the other social sciences - economics, sociology, political science, psychology.
``Most of the other social sciences have left that approach behind,'' says Preston, an Amherst College graduate who studied sociology at the University of Pennsylvania and holds the rank of Professor of Sociology. ``They are much more theoretically oriented.''
The demographer's approach to social issues has landed Preston squarely in the middle of controversy. In 1984, the nation's elderly took exception to his presidential address before the Population Association of America., a version of which appeared in Scientific American. In it, he noted that federal spending on children in the United States is less than one-tenth the amount spent on the elderly. Noting that the latter is largely consumption but that spending on children includes significant amounts of investment, he raised the possibility that there may be ``a direct competition between the young and the old for society's resources.''
Equally controversial is his current study of the hereditary basis for intelligence as measured by IQ, although the results are broadly encouraging. His work demonstrates, he says, that ``even if lower-IQ people produce twice as many children as higher-IQ people, the IQ distribution does not deteriorate from generation to generation.'' While that conclusion seems ``counter-intuitive,'' he says, the mathematics of the so-called ``stable population model'' support his case. ``There's this great fear that we're going to go into a perpetual decline. That's wrong. The IQ distribution reaches a stable equilibrium after a couple of generations.''
Why is that finding important? Because, he says, ``so many people have misunderstood the genetics of population change'' - including the Nazis in the 1930s, who made it ``a very important part of their platform.''
OF particular interest to Preston are changes in the US family. As indicators, he notes that:
Today, 23 percent of all births are out of wedlock, versus 5 percent in the 1950s.
Half of today's marriages are preceded by cohabitation.
On average, the birth rate is 1.8 children per woman - a figure unchanged for the last 15 years, and well below the 2.1 children per couple that demographers call the ``replacement rate.''
Soon there will be more 70-year-olds than infants. The average 40-year-old couple will have 2.88 living parents but only 1.78 living children.
Such signs suggest to Preston that ``some fundamental changes have affected the way we think about our adult lives.'' These include the role of children in parents' lives. There's no evidence, he says, that ``mothers are not as closely attached to their children as they always were.'' What's missing are the fathers.
``Men, on average, are playing a much less substantial role in family structures. I think it reflects a change in the basic value structure of American society - more emphasis on self-fulfillment, less emphasis on satisfying social expectations.''
That shift colors society's views of children. Citing survey research comparing parents' attitudes toward children in 1957 and 1976, Preston notes that the earlier group liked children who were obedient, industrious, and performed well in school. ``Those things had basically dropped out of the picture by 1976,'' he notes - replaced by such qualities as ``affectionate, loving, gets along will with siblings, good personality.''
``We've moved toward much more concern with psychological development and interpersonal relationships, and much less emphasis on success and achievement in school,'' he notes. At the same time, the research suggests that ``children are seen as more of a threat to the autonomous functioning of adults.''
What issues will shape demography in the 21st century? Preston, who led a working group in the National Academy of Sciences in 1985 that studied emerging research areas in demography, notes that the field will continue to be driven by the world's ``main population issues.'' These include the changing household and family structure, immigration, the social and behavioral aspects of health problems, and medical, demographic, and fertility changes in developing countries.
He foresees that rapid population growth in the developing countries will continue to ``throw huge resources into the fields of population studies and family planning programs.'' But ``in this country and in Western Europe the key concern over the next 20 years is going to be below-replacement fertility.
``No population, no nation, wants to see its population decline,'' he observes. Yet a number of Western countries are already declining, and the US population will start to decline in about 35 years. As that happens, ``we may get into questions of what it would take to have women bear more children - questions we have shied away from.''
Also on the horizon, he says, is a greater use of the techniques of demography to explore changes in values. Such things can be best measured indirectly, he says, ``by asking not what your values are, but what you think about other people's behaviors - what do you condemn, what do you support? How far are you willing to go in shunning somebody who has violated a norm of yours?''
What would he say to a 10-year-old to explain his own interest in the field?
``The excitement comes from the rather precise measurement of human behavior and the curiosity about what's driving it. If you enjoy the study of human behavior and you have a knack for numerical analysis, this is a field that might prove very attractive.''