If it's the number with the rating, I would submit that only a small
percentage of them are both current and proficient.

I'd be interested in seeing some statistics on this. Got a cite?

I know Richard Collins (Flying mag's ancient wag) has discussed this
many times, and I know that of my personal instrument pilot
acquaintances, very few, indeed, are current and proficient. (Most
fly VFR only, or very, VERY "soft" IFR.)

What we need, however, are statistics -- and I don't have any. How
could one track this?

It surely won't be in the insurance company statistics, since every
pilot has an incentive to claim to be the Ace of the Base on those
forms -- and the FAA is almost useless when it comes to hours flown
each year, IFR or VFR.
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"