For the following five exercises, you will need to construct indicator variables to use categorical variables as explanatory variables in logistic regression. Be sure to review the material in Chapter 11 on models with categorical explanatory variables (pages 571-575) before attempting these exercises.

Question 17.36

17.36 Sexual imagery in ads.

Refer to Exercise 17.20 (page 17-18) concerning the use of sexual imagery in magazine ads. Here is the two-way table of counts for the 1509 ads.

Magazine readership
Model dress Women Men General interest Total
Not sexual 351 514 248 1113
Sexual 225 105 66 396
Total 576 619 314 1509

Use the model dress, expressed as the odds that the dress is sexual, as the response variable and the magazine readership as the explanatory variable. Because there are three magazine readership categories, you will need two indicator variables for this multiple logistic regression analysis. Use the last category, general interest, for the “other” designation when creating these indicator variables.

imagery

  1. A friend has suggested that the three magazine categories be coded as 1, 2, 3 and that this single variable be used as the explanatory variable in the logistic regression. Explain why this analytical strategy is wrong.
  2. Summarize the results of the significance testing. Do the data support the idea that the sexual content expressed in the model dress varies by the magazine readership?
  3. Use the estimates for your model and the coding that you used for the explanatory variables to give the estimated log odds for each type of magazine readership.