Practice problems for computing DP. Answers at bottom of page. This is all made-up data.

1.

 
Has Disease
Does not have Disease
Symptom present
10
10
Symptom not present
0
20

What is the contingency between the symptom (predictor) and the disease (outcome)? Is the symptom a positive indicator of the disease?

2.

 
Economy improves
Economy does
not improve
Increase taxes
15
85
Leave taxes same
50
30

What is the contingency between increasing taxes (predictor) and improving the economy (outcome)? If true, should we increase taxes?

3.

 
Got a job within 6 months of graduating
Did not get a job within 6 months of graduating
Majored in engineering
160
40
Did not major in engineering
400
1600

What is the contingency between one's major (predictor) and getting a job (outcome)? Should one major in engineering?

4.

 
Lost weight
Did not lose weight
Exercised 3 times per week
8
2
Did not
100
900

What is the contingency between exercise (predictor) and losing weight (outcome)? Should you exercise?

5.

 
Gets the flu this year
Does not get the flu this year
Gets at least 7 hours of sleep
16
64
Does not get at least 7 hours
30
30

What is the contingency between being well rested (predictor) and getting the flu (outcome)? Should you sleep more in order to avoid contracting the flu?

 

 

 

 

 

 

 

Answers

1. DP = .50; yes, it is an imperfect positive indicator that the patient might have the disease.

2. DP = -.475; no, you should not increase taxes in order to improve the economy.

3. DP = .60; yep, engineering majors are in a good position for getting a job.

4. DP = .70; unfortunately, yes we should.

5. DP = -.30; yes, sleeping more will reduce the likelihood of getting the flu.