Answer
It is an observational study.
Work Step by Step
The families are volunteered to join the investigation.
Introductory Statistics 9th Edition
by Mann, Prem S.
Published by
Wiley
ISBN 10:
1-11905-571-7
ISBN 13:
978-1-11905-571-6
Chapter 1 - Section 1.6 - Design of Experiments - Exercises - Page 22: 1.33
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