Whereever I have lived in my adult life, the city has been extraordinarily quiet from Christmas to New Year’s — indeed, the quiet starts somewhat before Christmas. The natural explanation is that people go away for the holidays. (Students obviously do, but it’s far quieter than even at other times when students are on vacation.) The problem is, they must go somewhere, so it can’t be that every place empties out. (Obviously, some of the apparent quiet is simply the absence of traffic from people going to work, shopping, etc. When shops and restaurants close down in late December because of lack of customers it’s a bit self-fulfilling.) So why is it that I’m always in the places that people flee for the holidays?
A common pattern is that younger people with children travel to their parents, in their old home towns. In general, if there is a pattern of migration from some places X to other places Y, the sort of people who move around (like myself) will tend to be living at Y. At Christmas, then, the migration is temporarily reversed, and people travel from Y to X. For a brief time, Y empties out and X gets full. (Even 2000 years ago Joseph and Mary had to go back to their home town for Christmas. And, as we know, the town was full up.) So, people like me notice that whereever they happen to be living is one of the places that empties out, because of the selection bias. People of my parents’ generation are generally living in places that take in visitors at Christmas, and so perhaps seem livelier than at other times of the year.