sample size

yes, siva u r right - more the volume and data, better the analyses.
bank nifty options volume is much lesser than that of nifty.
i have lesser trouble in analysing nifty than BN.
even in BN stocks, pnb is traded so shallow in options that it is virtually impossible to analyse.
cnx it options has almost no volume.
having said that, it would be suffice to say
that the sample size we have for BN is enough to judge to tolerable accuracy.
for nifty, the sample size for analyses is perfect.
one more thing that needs to be kept in mind is
that only creamy layer of retail traders know the head or tail of options.
so even if the BN volume is less (not ridulously less though)
it represents fair picture of bank nifty.
a 10 megapixel camera gives a much sharper picture than a 1.3 or 2 megapixel camera but you can still recognize who's there in the picture and what he or she is upto. though if you want to zoom the picture and check out the details, you will have difficulty.
but even in this case, there are software to enhance a low pixel picture just like we have technicals to digitally enhance the option picture.
remember one thing, option data spread gives insight into operators minds which futures spread (there is hardly any spread there) can't even think of.
excellent question!