I'm not even sure how to formulate this right, so please forgive the generic
thread title.

I'm racking my brains trying to come up with a formula for an analytical
spreadsheet I'm working on. What I need to do, and haven't been able to
figure it out, is to count how many occurrences o X I have, excluding some
cells, and represent that in a percentage of the total.

To give a clearer picture, I have many columns with years. Say, 2008, 2007,
2006, and so on. Each year has, say, either X or Y. Now I can figure out the
times X occurs, and its percentage of total, no problem. But what I can't see
how to formulate, is getting the total and percentage of total since a given
year. For instance, if my spreadsheet has years going back to 1980, I want to
get a percentage of the total since 1995 only.

Am I being clear? It makes sense to me...