Research Methods: Brief Notes on qualitative methods, including
participant observation.
UCeL: Notes and video materials relating to observational methods.
In the book we outline an aspect of the "observer effect" related to
Elton Mayo's famous "Hawthorne Study" in the 1920's. The two sites linked
here allow you to explore this study in more detail:
Hawthorne Study: Detailed
outline of research, findings and conclusions.