The correct answer to this open question is the following.
The flaw that the Hawthorne study had and the way it affected the study's outcome was the following.
The Hawthorne effect was flawed in the study design. They should have used a "blind study" to measure the variables the researchers wanted to test. In that case, some participants wouldn't be notified that they were being observed. Another option could have been that the researchers formed a "control group," where the participants knew they were observed but also did not received any special treatment. Another flaw was the size of the experiment. It was small. Another possibility is that the researches might have misinterpreted the final results.
