We should start by gathering statistically valid estimates based on random, replicated samples of adequate size so we at least measure what sorts of variance our methods produce. (wattsupwiththat.com)
William Fifer, a professor of medical psychiatry at Columbia University Medical Center in New York City, said, «I think this gives us a much more valid estimate of the prevalence of these disorders.» (health.com)
The long term trend test of the National Assessment of Educational Progress (LTT NAEP) is the longest running test of student achievement that provides a scientifically valid estimate of what American students have learned. (educationnext.org)