¥F-test for Lack of Fit (lof)
HIf repeated measurements are available (and they should be), a Lack Of Fit (lof) test is first carried out.
åHypothesis:
HH0: E(Y) = b0 + b1X1 + b2X2 + É,+ bp-1Xp-1
HHa: E(Y) ­ b0 + b1X1 + b2X2 + É,+ bp-1Xp-1
å
åHypothesis is tested by comparing the variance of the modelÕs lack of fit to the measurement variance at each point (pure error).
åIf Flof is significant then model is inadequate. STOP HERE.
íReconsider independent variables, try again.
åIf Flof is insignificant then model appears adequate, so far.
åIt is important to test for the lack of fit:
íThe remainder of the analysis assumes an adequate model is used
íYou will not be visually inspecting the goodness of the fit for thousands of voxels!