So unless I only use YL for every mailing of a campaign, then do an identical campaign that has the same group and same number of mailings with only postcards, it is very difficult to quantify.

I just started mailing to out of state absentee owners too, but if there is some quantifiable data that shows mailing on X day is best, I'm all over it.

"Statistical significance helps quantify whether a result is likely due to chance or to some factor of interest,” says Redman.