Few creatures are less admired than the reviewer who faults a book, not for what it contains, but for what the author has chosen not to do. Into such company I reluctantly enter, for there is no other way to deal with Christopher Jencks' new book. Taken solely on its contents, "Who Gets Ahead?" offers little for the layman to complain about -- but even less to justify attention outside the world of academic sociology. Its importance for the general public lies almost wholly in what it leaves unsaid.

The purpose of this study, Jencks says in the introduction, is "to assess the efforts of a man's characteristics when he enters the labor market on his subsequent success." Toward this end, Jencks and his 11 coauthors (Susan Bartlett, Mary Corcoaran, James Crouse, David Eaglesfield, Gregory Jackson, Kent McClelland, Peter Mueser, Michael Olneck, Joseph Schwartz, Sherry Ward and Jill williams) fed data from 11 sociological surveys into their computers and analyzed the results. In one way or another, each of those surveys concerned individual economic "success" and the factors that predict and cause it. By combining and comparing the results, they attempt to show how an adult male's earnings and occupational status are connected to his family background and education as a child.

The harvest of this effort fills more than 300 pages of text and dozens of tables and charts, but if all the statistical elaborations and methodological nit-pickings were boiled away, the book's message would fit into about five pages of normal prose. (Daniel Yankelovich summarized the findings in a shorter article in Psychology Today, which most readers will find more useful than the book itself.) Indeed, the results can be summed up in two or three sentences without doing too much violence to the subtlety of the ideas.

There are various factors that effect the prospects for adult economic success. They include family background, "native" ability, years of schooling, and personality traits such as "leadership" and "dependability." No one of these traits is decisive by itself; many of them tend to be associated, both casually and coincidentally, with others on the list. The chances for success are skewed by factors such as race (and, presumably, sex, although the data are limited to men); the more of the positive factors you have working in your favor, the more likely you are to "get ahead."

Such less-than-startling conclusions are embedded in a dense, technical prose, which will yield its meaning only to readers who can easily explain the difference between a correlation and a multiple regression. Although it is being advertised as a trade book, this is a specialized treatise for a limited audience.

There is, I suppose, occasional value to this careful effort to see just how much each of the background factors is worth. For example, Jencks' data knocks down Richard Herrnstein's much-misunderstood theory of inherited abilities. Six years ago, in a book widely and unfairly denounced as a racist tract, Herrnstein warned that the United States was in danger of becoming a hereditary "meritocracy," in which smart people would get the best jobs, would marry other smart people and would produce smart children who would dominate their less able competitors. But according to the surveys in Jencks' book, there is almost as much variation in success among men of a certain "intelligence" level as among the population as a whole. "This suggests that the United States cannot be considered a 'meritocracy' at least if 'merit' is measured by general cognitive skills," the book says in one of the few sentences that slip the bonds of deadpan observation. "Nor do they offer much support for the part of Herrnstein's syllogism which assumes that ability is an important determinant of occupational success."

The book also points out that being raised in the South or on the farm is a big handicap; that children's aptitude test scores in the sixth grade (or even the third) predict their success nearly as well as tests in high school; that high school students whose "personality traits" lead them to participate in team sports, school newspapers, debating teams and religious groups have a better chance for success than those who join farm clubs, military drill units or political organizations. One of the few truly startling findings concerns adopted sons. Even though an adoptive "father" has absolutely no genetic influence over the abilities of his son, the connection between the father's status and the son's success was virtually the same, whether the child was biological or adopted.

When all the pieces are put together, they amount to confirmation of the timeless principle: the best way to get ahead is to choose the right parents. Sons born into the most privileged 20 percent of all families can expect to earn three times as much when they grow up as sons born into the lowest 20 percent.

But we knew this already, though perhaps not with such precision. The question is: So what? and here the authors are intentionally mute. One of the "so whats" is what, if anything, the government should do to increase "equality," of either opportunity or result. Jencks closes the book with a restatement of the prescription that caused such a furor when he introduced it seven years ago in "inequality": If we want to redistribute income, the most effective strategy is probably still to redistribute income." In other words, fairer competition for places in medical school will not do much to change the social structure if doctors still earn 10 times as much as schoolteachers. To me, the more interesting question is how the forces so minutely quantified in this book shape the patterns of real human lives -- what we count as "success" or "failure," the way we compare ourselves with others, the grails we choose to pursue. To such questions the surveys are as accurate, but as limited, a guide as a calorie chart would be to a feast of Brillat-Savarin.