  The effect of the length of inflation on the power spectra of scalar and
tensor perturbations is estimated using the power-law inflation model with a
scale factor of a(t) = t^q. Considering various pre-inflation models with
radiation-dominated or scalar matter-dominated periods before inflation in
combination with two matching conditions, the temperature angular power
spectrum (TT) and temperature-polarization cross-power spectrum (TE) are
calculated and a likelihood analysis is performed. It is shown that the
discrepancies between the Wilkinson Microwave Anisotropy Probe (WMAP) data and
the LCDM model, such as suppression of the spectrum at l = 2,3 and oscillatory
behavior, may be explained by the finite length of inflation model if the
length of inflation is near 60 e-folds and q > 300. The proposed models retain
similar values of chi^2 to that achieved by the LCDM model with respect to fit
to the WMAP data, but display different characteristics of the angular TE power
spectra at l < 20.
