  We have derived star formation rates (SFRs), gas-phase oxygen abundances and
effective dust absorption optical depths for a sample of galaxies drawn from
the Stromlo-APM redshift survey using the new Charlot and Longhetti (2001;
CL01) models, which provide a physically consistent description of the effects
of stars, gas and dust on the integrated spectra of galaxies. Our sample
consists of 705 galaxies with measurements of the fluxes and equivalent widths
of Halpha, [OII], and one or both of [NII] and [SII]. For a subset of the
galaxies, 60 and 100 micron IRAS fluxes are available. We compare the star
formation rates derived using the models with those derived using standard
estimators based on the Halpha, the [OII] and the far-infrared luminosities of
the galaxies. The CL01 SFR estimates agree well with those derived from the
IRAS fluxes, but are typically a factor of ~3 higher than those derived from
the Halpha or the [OII] fluxes, even after the usual mean attenuation
correction of A_Halpha=1 mag is applied to the data. We show that the reason
for this discrepancy is that the standard Halpha estimator neglects the
absorption of ionizing photons by dust in HII regions and the contamination of
Halpha emission by stellar absorption. We also use our sample to study
variations in star formation and metallicity as a function of galaxy absolute
bJ magnitude. For this sample, the star formation rate per unit bJ luminosity
is independent of magnitude. The gas-phase oxygen abundance does increase with
bJ luminosity, although the scatter in metallicity at fixed magnitude is large.
