  The incidence of intra-night optical variability (INOV) is known to to differ
significantly among different classes of powerful active galactic nuclei (AGN).
A number of statistical methods have been employed in the literature for
testing the presence of INOV in the light curves, sometimes leading to
discordant results. In this paper we compare the INOV characteristics of six
prominent classes of AGN, as evaluated using three commonly used statistical
tests, namely the $\chi^2-$test, the modified $C-$test and the $F-$test, which
has recently begun to gain popularity. The AGN classes considered are:
radio-quiet quasars (RQQs), radio-intermediate quasars (RIQs), lobe-dominated
quasars (LDQs), low optical polarization core-dominated quasars (LPCDQs), high
optical polarization core-dominated quasars (HPCDQs), and TeV blazars. Our
analysis is based on a large body of AGN monitoring data, involving 262
sessions of intra-night monitoring of a total 77 AGN, using 1-2 metre class
optical telescopes located in India. In order to compare the usefulness of the
statistical tests, we have also subjected them to a `sanity check' by comparing
the number of false positives yielded by each test with the corresponding
statistical prediction. The present analysis is intended to serve as a
benchmark for future INOV studies of AGN of different classes.
