The fertility stat, or possibly the algorithm that uses it, is broken. The wiki states that impregnation is a flat percentage chance equal to the sum of both partners’ fertility ratings, but in my experience the actual chance of a successful impregnation are much, much lower.
Im not sure its broken.
I suspect its relatively low even at max stats, this is to allow for traits to still have an impact.
This one for example. is it 2% per fail or just +2% on the second attempt?
Stats start at around 50 and max out at 1000?
This means at 50 its cant be 0% and at 1000 it cant mean 100%
If i was to guess id suspect a minimum 5% and maximum 50%
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Quick test:
1. Fertility = 385 vs 210 = 10 attempts, 9 fails 1 success = 10%
2. Fertility = 385 vs 220 = 10 attempts, 10 fails = 0%
3. Fertility = 392 vs 220 = 10 attempts, 10 fails = 0%
4. Fertility = 399 vs 230 = 10 attempts, 8 fails 2 success = 20%
5. 399 / 240 = 9 1 = 10%
6. 406 / 245 = 6 4 = 40%
7 413 / 250 = 8 2 = 20%
Now after writing all that down i realize its basically useless because not only do stats grow but its all chances. haha