County moth datasets tend to be large and 'messy' affairs - messy in the sense that they are large aggregations of data from a variety of sources, collected using a variety of methods. Some people will run a mercury vapour trap all night long in their garden, several times a week; others will run an occasional actinic trap for a few hours on a nature reserve; others will just send in a few sightings of moths they've found by day. Is it possible to draw any overall conclusions about which moths are increasing or decreasing from this mass/mess of data?
In an attempt to look at this for the Berkshire moth database, I've set up some user queries for use in MapMate that compare numbers of records and of individuals of particular species against total numbers for the year. Full details and a download of the queries are here on my kitenet website. Here are the resulting graphs for Mottled Rustic, currently doing very poorly in Berkshire: