Over my 10 years throwing Halloween parties I've started to notice a very complex and interesting psychology around how late guests stay at the party. My goal, of course, is always to have a lot of people staying late, and there are a few sneaky methods I've come up with to encourage that. Or rather, to discourage leaving early.
One year, my party had a great turnout and was in full swing, going spectacularly, when out of the blue around midnight there was a mass exodus and more than 50% of the guests left at once. I realized that a large group announced their departure nearby a collection of people and they all hopped on, starting a chain reaction. It's weird that people do that. So I've taken to asking a few of my closer friends to just "ghost" (leave without announcing it) if they feel like taking off while the party is still hot.
Another thing that's worked wonders is moving all sofas and chairs to the perimeters of the main party area and moving the food table to a central area. It keeps people standing and milling around rather than sitting, which makes one tired, which makes one think about going home. We did this for the first time last year and the party was in full swing past 2 am and didn't end until the sun was up.
Anyone else have good recommendations for encouraging late partying?