I consider annual medians to be a blunt spoon because of the different compositions of the datasets. That makes the monthly medians for the region the equivalent to using a snowshovel. Doing monthly medians by zip is like using a plow. For purposes of comparison I personally think it’s a waste of time.
The only reason I look at monthly sales by zip of a few areas is to get *an idea* of the percentages of forced sales and what trends there are on discounting and such. Even that type of analysis is anecdotal in nature, not what I’d call reliable.
I also like to follow volumes of sales and compare those numbers to similar periods in the past, but that’s also just a way to get a reading on the general trends. It’s not specific.
The way I’d get specific about a market’s pricing trends is to do a house-to-house comparison comparing the same house against its competition during the different periods of time.