Okay.
It ain't health, education, transportation, social security, supply, corporate salaries, government salaries, game level, country stock quality, employment, population size, tax rates, etc.
Let's talk about what it is . . .
1. It is a factor that is affecting my entire empire on LU, an empire-wide modifier.
2. It is not affecting my empire on GR. therefore, it is not a game-wide change.
3. The tendency is toward about 116 Welfare (a little below), up for some, down for others. A little over 10% change from the top.
I remember selling countries probably around the time the index began dropping so . . . this may be related to SSRCP's point about population sales effecting the index. Maybe country sales effect the index? If so, waiting should cure the problem, right?