  We address the highly debated issue of constraining the gamma-ray emission
region in blazars from cross-correlation analysis using discrete correlation
function between radio and gamma-ray light curves. The significance of the
correlations is evaluated using two different approaches: simulating light
curves and mixed source correlations. The cross-correlation analysis yielded 26
sources with significant correlations. In most of the sources, the gamma-ray
peaks lead the radio with time lags in the range +20 and +690 days, whereas in
sources 1633+382 and 3C 345 we find the radio emission to lead the gamma rays
by -15 and -40 days, respectively. Apart from the individual source study, we
stacked the correlations of all sources and also those based on sub-samples.
The time lag from the stacked correlation is +80 days for the whole sample and
the distance travelled by the emission region corresponds to 7 pc. We also
compared the start times of activity in radio and gamma rays of the correlated
flares using Bayesian block representation. This shows that most of the flares
at both wavebands start at almost the same time, implying a co-spatial origin
of the activity. The correlated sources show more flares and are brighter in
both bands than the uncorrelated ones.
