In a famous research study conducted between 1927 and 1932 at an electrical-equipment manufacturing plant, experimenters measured the influence of a number of variables (brightness of lights, room temperature, group pressure, working hours, and managerial leadership) on the productivity of the employees. the major finding of the study was that no matter what experimental treatment was employed, the production of the workers seemed to improve. it seemed as though just knowing that they were being studied had a strong positive influence on them. an important statistical effect was named for this manufacturing plant. what is it?