Multiple Regression and Dummy Variables

EXAMPLE: Salamanders and oxygen uptake

Ruben and Scott (1989) note a positive correlation between lung volume and head width, due to the mechanism of salamander breathing. Consequently, lunged salamanders with relatively wider heads tend to absorb a smaller proportion of their oxygen cutaneously. Many salamanders have no lungs, however, and among them head size appears unrelated to cutaneous oxygen uptake.

TOPICS:

A single regression model to describe these ideas
The role of Dummy variables
The partial F-test, overall F-test and t-tests in multiple regression
Combined versus separate analyses
Confidence Intervals and Prediction Intervals

SAS commands and data

data sasuser.sal;
input IndLung OXY WIDTH;
LxW = IndLung*WIDTH;
datalines;
 0         81                .13
 0         84                .13
 0         76                .16
 0         86                .19
 1         45                .23
 1         49                .23
 1         64                .17
 1         65                .16
 1         69                .16
 1         74                .14
run;

HANDOUTS: