The Durbin-Watson statistic is a statistic for detecting first-order serial correlation in the residuals 
, ..., 
of a regression. It is defined
by
 |
It satisfies 
,
with values near 2 indicating little first-order autocorrelation. If 
is the lag-one residual autocorrelation,
then 
.
The null distribution depends on the regression design, and the usual Durbin-Watson inference is not generally valid when a lagged dependent variable is included among the regressors.
