This tutorial addresses possible sources of confusion in interpreting trait scores from the bifactor model. The bifactor model may be used when subscores are desired, either for formative feedback on an achievement test or for theoretically different constructs on a psychological test. The bifactor model is often chosen because it requires fewer…

Two computer viruses that have caused hundreds of millions of dollars in damage over the past four years are the Melissa and the Sasser virus. In March of 1999, the Melissa virus first appeared on the Internet and spread rapidly throughout computer systems in the United States and Europe. The virus made its way through 1.2 million computers in the…