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Each observation in the following data set shows a person\'s income (measured in

ID: 3063327 • Letter: E

Question

Each observation in the following data set shows a person's income (measured in thousands of dollars) and whether that person purchased a particular product last year. Assign a zero for a No purchase and a 1 for a Yes, and estimate a logit model for the purchase of this product. Write down the estimated logit model; and calculate the probability of buying the product if income is $40 (i.e., $40,000) and if income is $70 (i.e., $70,000). Calculate and interpret the meaning of the odds ratio if income changes from $70 to $71. What is the value of the concordance index and its meaning?

Person

Income (000)

Purchase

1

$31

No

2

$50

No

3

$33

No

4

$77

Yes

5

$54

Yes

6

$78

Yes

7

$21

No

8

$46

Yes

9

$66

No

10

$89

Yes

Person

Income (000)

Purchase

1

$31

No

2

$50

No

3

$33

No

4

$77

Yes

5

$54

Yes

6

$78

Yes

7

$21

No

8

$46

Yes

9

$66

No

10

$89

Yes

Explanation / Answer

With the given data, the logistic model is

Purchase = exp(-4.98858 + (0.09213*Income))/(1 + exp(-4.98858 + (0.09213*Income)))

When the income is 40,000, the estimated probability is 0.2136 and when income is 70,000 the estimate probability is 0.8116

The odds ratio when income changes from 70 to 71 is 1.01686 which means that you are 1.01686 times more likely to purchase when your income is 71000 than when your income is 70000

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