'Rags-to-riches' isn't common -- not even in the NBA

As the NBA season gets underway, there is no doubt that the league's best player is 6-foot-8 LeBron James, of the Miami Heat. James was born poor to a 16-year-old single mother in Akron, Ohio. The conventional wisdom is that his background is typical for an NBA player. A majority of Americans, Google consumer survey data show, think that the NBA is composed mostly of men like James. But it isn't.

I recently calculated the probability of reaching the NBA, by race, in every county in the United States. I got data on births from the Centers for Disease Control and Prevention; data on basketball players from basketball-reference.com; and per capita income from the census. The results? Growing up in a wealthier neighborhood is a major, positive predictor of reaching the NBA for both black and white men. Is this driven by sons of NBA players like the Warriors' brilliant Stephen Curry? Nope. Take them out and the result is similar.

But this tells us only where NBA players began life. Can we learn more about their individual backgrounds? In the 1980s, when the majority of current NBA players were born, about 25 percent of African-Americans were born to mothers younger than 20; 60 percent were born to unwed mothers. I did an exhaustive search for information on the parents of the 100 top-scoring black players born in the 1980s, relying on news stories, social networks and public records. Putting all the information together, my best guess is that black NBA players are about 30 percent less likely than the average black male to be born to an unmarried mother and a teenage mother.

Need more evidence? The economists Roland G. Fryer and Steven D. Levitt famously studied four decades of birth certificates in California. They found that African-American kids from different classes are named differently. Black kids born to lower-income parents are given unique names more often. Based on searches on Ancestry.com, I counted black NBA players born in California in the 1970s and 1980s who had unique first names. There were a few, like Torraye Braggs and Etdrick Bohannon. But black NBA players were about half as likely to have a unique name as the average black male.

From 1960 to 1990, nearly half of blacks were born to unmarried parents. I would estimate that during this period roughly twice as many black NBA players were born to married parents as unmarried parents. In other words, for every LeBron James, there was a Michael Jordan, born to a middle-class, two-parent family in Brooklyn, and a Chris Paul, the second son of middle-class parents in Lewisville, N.C., who joined Paul on an episode of "Family Feud" in 2011.

These results push back against the stereotype of a basketball player driven by an intense desire to escape poverty. In "The Last Shot," Darcy Frey quotes a college coach questioning whether a suburban player was "hungry enough" to compete against black kids from the ghetto. But the data suggest that on average any motivational edge in hungriness is far outweighed by the advantages of kids from higher socioeconomic classes.

What are these advantages? The first is in developing what economists call noncognitive skills like persistence, self-regulation and trust. We have grown accustomed to hearing about the importance of these qualities for success in school, but players in team sports rely on many of the same skills.

The second relevant advantage of a relatively prosperous upbringing is height. The economist Robert W. Fogel has demonstrated the impact of improved early life nutrition on adult height over successive generations. Poor children in contemporary America still have substandard nutrition, holding back their development. They have higher infant mortality rates and lower average birth weights, and recent research has found that poverty in modern America inhibits height. In basketball, the importance of every inch is enormous. I estimate that each additional inch almost doubles your chances of making the NBA.

The NBA's changing demographics may also reflect the advantages of growing prosperity. Even casual fans will have noticed the difference the past 30 years have made: In 1980, fewer than 2 percent of NBA players were foreign-born; now more than 20 percent are.

Much of this is surely because of the increased international popularity of basketball. In 1992, a 14-year-old German, Dirk Nowitzki, watched the American team starring Jordan, Larry Bird and Magic Johnson win a gold medal in the Barcelona Olympics. Nowitzki, a childhood tennis and handball star, decided he wanted to become a basketball player. But there is a somewhat surprising factor that may also be contributing to the game's internationalization: Foreign countries are producing taller men.

From 1900 to 1980, the average American adult male's height rose to 5-foot-10 from 5-foot-6. But American height has leveled off since 1980. The number of American-born 7-foot NBA players, which increased from one in 1946, the NBA's first year, to 16 in 1980, has leveled off as well (there were 20 last year). Western countries that have health patterns similar to those of the United States have also produced a fairly constant number of 7-foot NBA players during the past few decades.

Meanwhile, other countries have caught up to the United States in health and height. A widely available proxy for early life conditions is infant mortality. In the United States, roughly 20 fewer infants per 1,000 births died in 2012 than in 1960. In other countries, declines have been much larger. In Turkey, over the same period, the rate dropped by a staggering 159 per 1,000 births. Even some Western European countries, like Spain, Greece and Portugal, had declines more than twice as large as those in America. All of these countries, recent research finds, have grown taller.

Or look at it from the other direction. Suppose Omer Asik, a 27-year-old Turkish player on the Houston Rockets, was born 25 or 30 years earlier, when Turkey's children were much worse off. Perhaps he would have peaked as a 6-foot-10 forward in Ankara, not as a 7-foot center in Houston.