  We compare the peculiar velocities derived from the I-band Tully-Fisher (TF)
relation for 989 field spiral galaxies in the SFI catalogue with the predicted
velocity field derived from the IRAS PSCz galaxy redshift survey. We assume
linear gravitational instability theory and apply the maximum likelihood
technique, VELMOD, to SFI galaxies within cz<6000 km/s. The resulting
calibration of the TF relation is consistent with a previous, independent
calibration for a similar sample of spirals residing in clusters. Our analysis
provides an accurate estimate of the quantity beta. Using the forward TF
relation and smoothing the predicted velocity field with a Gaussian filter of
radius 300 km/s, we obtain beta = 0.42 +/- 0.04 (1 sigma uncertainty). This
value, as well as other parameters in the fit, are robust to varying the
smoothing radius to 500 km/s and splitting the sample into spherical shells in
redshift space. The one exception is the small-scale velocity dispersion,
sigma_v, which varies from 200 km/s within cz= 4000 km/s 500 km/s at larger
distance. For beta = 0.42, the residuals between the TF data and the PSCz
gravity field are uncorrelated, indicating that the model provides a good fit
to the data. More generally, a chi^2 statistic indicates that the PSCz model
velocity field provides an acceptable (3 sigma) fit to the data for 0.3 < beta
< 0.5.
