
MODEL BUILDING 171
autocorrelation and a value of four indicates negative autocorrelation.
When a table is not available, a rule of thumb is that values of d between
1.5 and 2.5 indicates no autocorrelation. The Durbin- Watson test statis-
tic d is defined with the following equation:
Durbin- Watson Test Statistics
A couple of notes are in order regarding this formula. First, notice
that although we are testing for the significance of a correlation, nei-
ther a sample (r) or assumed population (ρ) correlation coefficient is
used in the calculations. Second, note that the top of the formula is
summed from “i = 2 to n” whereas the bottom i ...