We use archival data from the Phoenix Deep Survey to investigate the variable radio source population above 1 \mathrm { mJy } /beam at 1.4 \mathrm { GHz } .
Given the similarity of this survey to other such surveys we take the opportunity to investigate the conflicting results which have appeared in the literature .
Two previous surveys for variability conducted with the Very Large Array ( VLA ) achieved a sensitivity of 1 \mathrm { mJy } /beam .
However , one survey found an areal density of radio variables on timescales of decades that is a factor of \sim 4 times greater than a second survey which was conducted on timescales of less than a few years .
In the Phoenix deep field we measure the density of variable radio sources to be \rho = 0.98 \mathrm { deg } ^ { -2 } on timescales of 6 months to 8 years .
We make use of WISE infrared cross-ids , and identify all variable sources as an AGN of some description .
We suggest that the discrepancy between previous VLA results is due to the different time scales probed by each of the surveys , and that radio variability at 1.4 \mathrm { GHz } is greatest on timescales of 2 - 5 years .