Question 17.15

17.15 What's wrong?

For each of the following, explain what is wrong and why.

  1. If in a logistic regression analysis, we estimate that the probability of an event is multiplied by 2 when the value of the explanatory variable changes by 1.
  2. The intercept is equal to the odds of an event when .
  3. The odds of an event are 1 minus the probability of the event.

17.15

(a) It is not multiplied by 2. When the explanatory variable changes by 1, the odds are increased by a factor of e2 or 7.389 times. (b) It is missing the log; the intercept is equal to the log odds of an event when . (c) The odds of an event are the probability of the event divided by 1 minus the probability of the event.