Answer
Observational study.
Work Step by Step
The subjects are not deliberately assigned to specific treatments, thus it is an observational study.
The Basic Practice of Statistics 7th Edition
by Moore, David S.; Notz, William I.; Fligner, Michael A.
Published by
W. H. Freeman
ISBN 10:
146414253X
ISBN 13:
978-1-46414-253-6
Chapter 27 - One-Way Analysis of Variance: Comparing Several Means - Chapter 27 Exercises - Page 672: 27.33c
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