March 19, 2003
Lab Assignment # 7
Due: Week of March 26, 2003

Logistic Regression

Refer to the data in Table 11.24 (FW11P05) of your textbook.  Scientists propose that the size of the ventricle (a physiological feature of the brain determined by an X-ray) may be associated with an abnormal EEG (brain wave) reading.  The size of the ventricle was determined for elderly patients, and then the EEG was labeled as normal (0) or abnormal (1).

SAS Program

  1. Construct a scatterplot relating EEG reading to size of the ventricle with proc plot.
  2. Use proc logistic to perform a logistic regression predicting EEG reading based on size of the ventricle. Use the following SAS commands:
     

proc logistic data=______ descending;
                        model eeg = vent;
                        run;

Assignment

  1. What is the apparent relationship between ventricle size and EEG (does the EEG tend to be normal with higher or lower ventricle size)?
  2. Report the estimated simple linear regression model.
  3. Use the model given above to calculate the probability of having an abnormal EEG when the ventricle size is 25 and when the ventricle size is 80.
  4. Report the odds ratio.  What does this tell you (what happens to the odds of getting an abnormal EEG when the ventricle size is increased by one unit)?