  We use a sample of 4178 Lyman break galaxies (LBGs) at z = 3, 4 and 5 in the
UKIRT Infrared Deep Sky Survey (UKIDSS) Ultra Deep Survey (UDS) field to
investigate the relationship between the observed slope of the stellar
continuum emission in the ultraviolet, {\beta}, and the thermal dust emission,
as quantified via the so-called 'infrared excess' (IRX = LIR/LUV). Through a
stacking analysis we directly measure the 850-{\mu}m flux density of LBGs in
our deep (0.9mJy) James Clerk Maxwell Telescope (JCMT) SCUBA-2 850-{\mu}m map,
as well as deep public Herschel/SPIRE 250-, 350- and 500-{\mu}m imaging. We
establish functional forms for the IRX-{\beta} relation to z ~ 5, confirming
that there is no significant redshift evolution of the relation and that the
resulting average IRX-{\beta} curve is consistent with a Calzetti-like
attenuation law. We compare our results with recent work in the literature,
finding that discrepancies in the slope of the IRX-{\beta} relation are driven
by biases in the methodology used to determine the ultraviolet slopes.
Consistent results are found when IRX-{\beta} is evaluated by stacking in bins
of stellar mass, M, and we argue that the near-linear IRX-M relationship is a
better proxy for correcting observed UV luminosities to total star formation
rates, provided an accurate handle on M can be had, and also gives clues as to
the physical driver of the role of dust-obscured star formation in
high-redshift galaxies.
