D.8 Answers: Designing observational studies
Answers to exercises in Sect. 8.6.
Answer to Exercise 8.1:
1. Randomly allocate students to receive either bottled or tap water,
and have them rate the taste.
Or,
randomly allocate students to receive bottled or tap water first,
then swap to the other type of water,
and each student would then provide two ratings.
2. The students would not be aware of which water they would be drinking.
3. Neither the students nor the researchers who give the students the water
would know which type of water the students are drinking.
4. We can’t really set up a control here.
5. Any of the random sampling methods are possible, and are preferred.
In practice, perhaps use a convenience sample,
but try to get a sample as representative
as possible (Sect. 5.9).
Answer to Exercise 8.2:
Yes.
Consider a study of the effect of smoking:
non-smokers are the control.
However, in an observational study, cases cannot be allocated to be controls.
Answer to Exercise 8.3:
No.
People can know they are being observed.
Answer to Exercise 8.4:
The descriptions indicates that patients probably
knew they were involved, so the Hawthorne effect
should be considered when interpreting the results.