1. Understanding Observational Studies
Lecture 9
Section 3.4
Mon, Sep 18, 2006

2. Types of Observational Studies
Retrospective study
Prospective study

3. Example Which studies were prospective? Which were retrospective?
Empathy study.
The Cocoa study.
Beer vs. wine study.
Gory images study.

4. Example
Example 3.7, p. 160 – High-fiber Diet Cuts Heart-attack Risk in Men.
High-fiber
diet
2375
22625
Low-fiber
diet
1260
Heart attack
16740
No heart attack
Population #1
p1 = 0.07
Population #2
p2 = 0.095

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

6. Example
Describe the design of this study had it been set up as a retrospective study.
High-fiber
diet
Low-fiber
diet
1260
2375
Heart attack
Population #1
p1 = 0.653
16740
22625
No heart attack
Population #2
p2 = 0.575

7. 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?

8. 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?

9. 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?

10. BAD Monograms
Do Bad Monograms Spell R.I.P.?