Here's a quick rarity guide on how the Simpsons Minifigures fall in the blind pack boxes.
I've gotten these numbers from various box breaks I've seen.
It appears that each minifigure falls at least 3 per box.
Common - 5 per box
Uncommon 4 per box
Rare - 3 per box
1. Homer - Common
2. Bart - Common
3. Marge - Common
4. Lisa - Uncommon
5. Maggie - Uncommon
6. Grandpa - Rare
7. Ned Flanders - Uncommon
8. Krusty - Uncommon
9 Milhouse - Rare
10. Ralph - Rare
11. Apu - Rare
12. Nelson - Rare
13 Itchy - Uncommon
14. Scratchy - Uncommon
15. Chief Wiggum - Rare
16. Mr. Burns - Rare