The authors broke down air pollution exposure into ranges (quartiles) and then presented odds of autism in relation to each exposure range for different time points.
Ibbotson has studied stock returns back to 1972 and says thinly traded stocks beat highly liquid ones of equal market values in all four quartiles ranked by size.
Twenty-one percent of students from the low socioeconomic group families were in vocational programs, but only 3 percent of students in the highest quartile and 13 percent of those in the middle two quartiles.
The difference in risk-adjusted returns averaged 7.5% a year, based on a subgroup of 2, 300 firms that reported sales and earnings growth sufficient to put them in one of the two quartiles for at least three years in a row.