As soon as anyone goes out to measure a process, things change. Everyone pays more attention. The process operators are more likely to closely monitor their process and quality inspectors are likely to be more effective in segregating defects. The resultant product you are sampling is not likely to represent that of a normal process. This is even true when people are polled on an issue, in that the answer may be the result of far more careful thought than the impulses or knee-jerk reactions that might guide those people in their daily actions.

There have been many studies done on how people react to having someone pay attention to them. Perhaps the most famous is the Hawthorne Study, which was done at a large Bell Western ...

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