  We investigate the infrared / radio correlation using the technique of source
stacking, in order to probe the average properties of radio sources that are
too faint to be detected individually. We compare the two methods used in the
literature to stack sources, and demonstrate that the creation of stacked
images leads to a loss of information. We stack infrared sources in the Spitzer
extragalactic First Look Survey (xFLS) field, and the three northern Spitzer
Wide-area Infrared Extragalactic survey (SWIRE) fields, using radio surveys
created at 610 MHz and 1.4 GHz, and find a variation in the absolute strength
of the correlation between the xFLS and SWIRE regions, but no evidence for
significant evolution in the correlation over the 24-um flux density range 150
uJy - 2 mJy. We carry out the first radio source stacking experiment using
70-um-selected galaxies, and find no evidence for significant evolution over
the 70-um flux density range 10 mJy - 100 mJy.
