From the documentation:
The Welfare Index is taking the lowest value of several other indexes:
The Health Index
The Education Index
The Transportation Index
The Supply Index + 41
The Employment Index + 37
The Social Security Index + 38
The Government Salary Index + 27
The Consumption Index contributes between 0 and 8 point to the welfare index. It needs to be at a level of about 300, to reach the max effect.
The game level will increase the welfare index by 1 point, for each game level higher than 10.