While researchers have long shown that tall people earn more than their shorter counterparts, it's not only social discrimination that accounts for this inequality -- tall people are just smarter than their height-challenged peers, a new study finds.

"As early as age three -- before schooling has had a chance to play a role -- and throughout childhood, taller children perform significantly better on cognitive tests," wrote Anne Case and Christina Paxson of Princeton University in a paper published by the National Bureau of Economic Research.

The findings were based primarily on two British studies that followed children born in 1958 and 1970, respectively, through adulthood and a U.S. study on height and occupational choice.

Other studies have pointed to low self-esteem, better health that accompanies greater height, and social discrimination as culprits for lower pay for shorter people.

But researchers Case and Paxson believe the height advantage in the job world is more than just a question of image.

"As adults, taller individuals are more likely to select into higher paying occupations that require more advanced verbal and numerical skills and greater intelligence, for which they earn handsome returns," they wrote.

For both men and women in the United States and the United Kingdom, a height advantage of four inches equated with a 10 percent increase in wages on average.

But the researchers said the differences in performance crop up long before the tall people enter the job force. Prenatal care and the time between birth and the age of 3 are critical periods for determining future cognitive ability and height.

"Prenatal care and prenatal nutrition are just incredibly important, even more so than we already knew," Case said in an interview.

Since the study's data only included populations in the United Kingdom and the United States, the findings could not be applied to other regions, Case said.

And how tall are the researchers?

They are both about 5 feet 8 inches tall, well above the average height of 5 feet 4 inches for American women.