The test was carried out with "a statistically valid sample" of 15,638 reservists assigned to 119 different units, the Pentagon said Friday.

"If we're suspicious," Mr. Stetson said, "we'll go to the school and ask if that's really a valid writing sample, or whatever."

The auditor would "randomly select" a "statistically valid" sample of claims (usually 30-50.)

Nancy Brown, Athenahealth's senior vice president for clinical service development, acknowledged that "it is not a statistically valid sample."

In using autopsies to assess quality of care, one problem involves random selection of cases to obtain statistically valid samples.

It is based on estimating a probability distribution representing what can be expected from valid samples.

Striking a balance between a statistically valid sample and minimum surveyor cost is not simple.

Ensuring that a statistically valid sample that will give a fair and accurate allocation presents a challenge.

"But this is the first statistically valid sample of what workers themselves think on a range of issues of particular interest to the commission."

For example, they might say that their telephone polls get too few blacks and Hispanics, forcing them to weight up the number of minorities to get a valid national sample.