Analyzing Employee Turnover - Predictive Methods

At first glance, 'intent to leave' seems like it should be pretty good predictor of turnover. If a coworker told me that they were going to quit, I feel like I'd have a pretty good sense of how likely they were to leave. However, many researchers have developed constructs to measure this intention and the results are surprising. For example, there was a meta-analytic study (i.e., study of studies) in 2000 by Rodger Griffeth and Peter Hom on turnover that found the construct'intent to leave' had a shared variance with actually leaving of 12% across all studies (explains roughly 12% of why people leave). That's pretty good for a study on human behavior, but it does leave a reader wondering what is going on.