# What does it mean in terms of regression if residuals are not white noise?

I need help in answering this one, it is an exam question.

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Are these supposed to be residuals from a fit of a time-series? That is often the context where the term "white noise" is used. –  gung Nov 24 '12 at 15:22

Strictly speaking, the residuals of a regression are not white noise. Since each residual is a function of the entire data set, the residuals are lightly correlated.

But ... there's correlation and there's correlation.

Residuals can fail to be "white noise" if:

• The regression model was not correctly specified. e.g $Y=a + bX + cX^2$ should have been chosen instead of a $Y=a+bX$.