Most of the human factor studies we

Most of the human factor studies were cause-effect. This appears to be a sign of maturity of the experimentalists in that area as well as the size and nature of the problem they were attacking. The project-based studies were dominated by correlational studies early on but have evolved to more descriptive (and qualitative) style studies over time. I believe this reflects early beliefs that the problem was simpler than it was and some simple combination of metrics could easily explain cost quality, etc