In the past year and 1/2 I've had 2 parties where people will say "Yes, we're coming" to a party then half of them not show, or they will only stay an hour before jetting off to someplace else. I end up with too much food and rather annoyed, but I guess it's my own fault for assuming the "yes" for a family of 5 only means 2 showing up.

Any suggestions on how to plan better?

By the way, the offending parties were family...not mine, his.