1. Understanding Observational Studies
Lecture 11
Section 3.4
Mon, Sep 10, 2007

2. Types of Observational Studies
Retrospective study
Prospective study

3. Example Which studies were prospective? Which were retrospective?
Case Study 1 – Empathy with cheaters.
Case Study 6 – Buying habits of beer and wine drinkers.

4. Example
Example 3.7, p. 160 – High-fiber Diet Cuts Heart-attack Risk in Men.

5. As a Prospective Study As a prospective study. Low-fiber diet 1600
23400
High-fiber
diet
1800
Heart attack
16200
No heart attack
Population #1
p1 = 10%
Population #2
p2 = 6.4%

6. Example
Describe the design of this study had it been set up as a retrospective study.

7. Example As a retrospective study. Low-fiber diet High-fiber diet 1800
1600
Heart attack
Population #1
p1 = 47%
16200
23400
No heart attack
Population #2
p2 = 59%

8. Prospective Studies
In a prospective study, the explanatory variable’s value is often its present value (but not always).
How would the researchers determine the values of the response variables?

9. Retrospective Studies
In a retrospective study, the response variable’s value is again often its present value (but not always).
How would the researchers determine the values of the explanatory variables?

10. Difficulties in Observational Studies
In an observational study,
The researchers cannot control the explanatory variables.
The researchers cannot control the confounding variables.
In the example about fiber vs. heart-attack risk, what are some plausible confounding factors?

11. Case Study 7
Monogrammic Determinism
Do Bad Monograms Spell R.I.P.?