California College San Diego Different Types of Breaks Discussion

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Learning Goals
Identify features of experiment design that control the effects of confounding
Explain how the study design impacts the types of conclusions that can be drawn
1) The Hawthorne Works, in Cicero, Illinois, was a large factory complex built by Western
Electric starting in 1905 and operating until 1983. It had 45,000 employees at the
height of its operations. Besides telephone equipment, the factory produced a wide
variety of consumer products, including refrigerators and electric fans. Hawthorne
Works was named for Hawthorne, Illinois, a small town that was later incorporated into
Cicero. The facility was so expansive; it contained a private railroad to move shipments
through the plant to the nearby Burlington Northern Railroad freight depot, and
workers regularly used bicycles for transit within the plant. It was purchased in the mid-
1980s by the late Donald L. Shoemaker and replaced with a shopping center.
(Wikipedia: http://en.wikipedia.org/wiki/Hawthorne Works)
In addition to its enormous output of telephone equipment, Hawthorne Works was the
site of some well-known industrial studies. In one of the studies, experimenters chose
two women as test subjects and asked them to choose four other workers to join their
respective test group. Together the women in each test group worked in a separate
room over the course of five years (1927–1932) assembling telephone relays.
Output was measured mechanically by counting how many finished relays each worker
dropped down a chute. This measuring began in secret two weeks before moving the
women to an experiment room and continued throughout the study. In the experiment
room, they had a supervisor who discussed changes with them and at times used their
suggestions. Then the researchers spent five years measuring how different variables
impacted the group’s and individuals’ productivity. (Wikipedia:
http://en.wikipedia.org/wiki/Hawthorne effect)
a) The researchers decided to study the effect of breaks on productivity. First they
provided the workers with two 5 minute breaks (after a discussion with the workers
on the best length of time), and then they changed to two 10-minute breaks (not
the workers’ preference). Productivity increased, but when the workers received six
5-minute breaks, the workers disliked it and reduced output.
Is this an observational study or an experiment? If it’s an observational study, what
population is being studied? If it’s an experiment, what is the treatment?
Part a) continued…
What are the explanatory and response variables?
Is the explanatory variable the only variable impacting the response variable? If not,
what are the confounding variables that impact the response variable?
b) Then the researchers decided to study the effect of the length of the workday on
productivity. They shortened the work day by 30 minutes and output increased. But
when they shortened it more, overall output decreased even though the output per
hour increased. When they returned to the first condition (prior to shortening the
work day by 30 minutes), output peaked.
What are the explanatory and response variables?
Is the explanatory variable the only variable impacting the response variable? If not,
what are the confounding variables that impact the response variable?