For years, educators have heard dire warnings about a supposed decline in the number of science, technology, engineering, and mathematics (STEM) graduates from U.S. colleges and universities, and the effect this could have on the nation's global competitiveness. Now, a new study suggests the problem might be different in nature than originally assumed.

The number of STEM graduates from U.S. schools continues to exceed the number of hires in these fields each year, the report says. Yet, researchers found the number of highest performing students moving on to STEM fields after graduation is declining.

The report, "Steady as She Goes? Three Generations of Students through the Science and Engineering Pipeline," explores the attrition rate of STEM students from high school to a career path, as well as changes in this attrition rate and changes in the quality of students who follow the STEM path.

Three points along the STEM pipeline are examined: the transitions from high school to a STEM degree in college (five years after high school), from the completion of a STEM degree to a first job (three years after college), and from the completion of a STEM degree to mid-career STEM employment (10 years after college completion).

"Overall, we don't see huge changes in supply, and that's the major headline," said Hal Salzman, professor of public policy at Rutgers University and the report's co-author. "The assumptions about dramatic change aren't there, and this is quite surprising to us."

Differences among various STEM fields do exist, but by the numbers, the supply of STEM-related workers has remained quite strong, he added.

Findings indicate that retention along the STEM pipeline remained strong, and even increased, from the 1970s to the late 1990s. The overall trend of increasingly strong STEM retention rates, however, is accompanied by simultaneous and sometimes sharp declines in retention among the highest performing students in the 1990s.

The study found that STEM retention rates at the three transition points from the 1970s to the late 1990s and the beginning part of this decade remained relatively unchanged from high school to college, increased from college to a first job, and increased from college to the mid-career point.

The highest STEM performers' retention rate increased from high school to college, but then decreased steeply thereafter. Their retention rate was no different from that of average performers between college and the first job, but then decreased "in absolute terms, as well as relative to the average trend," from college to mid-career jobs.

The report notes that the 1990s "marked a turning point in longer-term trends for the best students either in high school or college." Students who achieved top scores on standardized tests and who had the highest GPAs seemed to drop out of the STEM pipeline "at a substantial rate," with the decline appearing to have come on suddenly in the mid- to late-1990s.