Post by Throwaway001 in WonderfulWhims comments

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Hey! I'm having the same problem! My sims are not on birth control. I'm using the simple pregnancy mode. The percentage is 30% for both played sims and NPCs, but they've woohooed like 30 times. Both of them are played sims. I triple checked; one can impregnate and the other can be impregnated. There are four sims in the household. Both sims are human.

Other things to note: They were able to get pregnant ONCE and they had twins. Also, none of the other sims in the save have issues getting pregnant. Do you have any idea what this could be? My guess was that one of them had accidentally gotten the hypofertile attribute, but I checked their sim info using your built-in cheat and none of them had the trait.

Also, I tried having them woohoo with other sims and they didn't have a problem impregnating/being impregnated by the other sims; the problem only happens when they woohoo with each other. Please answer soon! I created this account specifically so I could get an answer from you!

Update: I've done some data mining. It seems to have to do with the percentages. When I set it to 40%, the sim gets pregnant 100% of the time, as do all other sims. When I set it to 30%, she gets pregnant 0% of the time while other sims get pregnant as usual.

TURBODRIVER3 years ago (1 edit)

Things sound about right. An important element to understand, is that even though you set the chance to 30%, it's not truly 30%, as each of the participants has to roll that chance. 30% is still pretty high, but can you roll it twice (one for the impregnator, one for the impergnated) with success? I get that this might not sound ideal, but this is made because using anything above 10% would often feel for majority of the users like using 99%.

With this logic, the probability of 30% is actually 9% (30% * 30%). The one that succeeds in your case, 40%, is actually 16%.

Throwaway0013 years ago

Thank you! I had no idea! I'll change the chance to a higher percent.

Tojaw3 years ago

Hi. Maybe that's not the right place to ask, but if this is how the pregnancy chances are calculated, how does the intersex mod work then? If I have the probability at 50%, the chance that one parent gets pregnant will be 25%. Is the chance that both parents get pregnant at 6.25% then? And is the chance to get one child 25% * 75% * 2 = 37.5%?

TURBODRIVER3 years ago

That's right, it would be 6.25% of getting both pregnant at a 50% probability. The number of children that get born is not affected, but if you're asking about just one Sim getting pregnant then that's 25%.

Tojaw3 years ago (2 edits)

So it first determines if Sim 1 impregnates Sim 2 (25%), then if Sim 2 impregnates Sim 1 (25%). So the chances are like having two WooHoos in a row...

Maybe decreasing the chance for a "Both" Sim to get pregnant when having sex with another "Both" Sim could push the probability of a child regardless of impregnator and impregnated down to 25%...

It's math time. I'll have to think, but I think that currently a "Both" couple has a higher chance of one getting pregnant than any other couple. I'll see if I can come up with a solution. Unfortunately I can only comment here because the other comment section is locked.

Edit: I got the solution. Whenever two "Both" Sims have sex, the fertility chance (the one you can set) has to be calculated according to this formula

sqrt( - sqrt( 1 - 2 * f^2 ) + 1 ) / sqrt( 2 )

with f being the set fertility chance (let's say 50%). Then it can be passed to the calculation of pregnancy.

The result is 38.27%, so the chance of Sim 1 impregnating Sim 2 is 38.27% * 38.27% = 14.64%. That's also the chance of Sim 2 impregnating Sim 1. As such, the chance of the WooHoo resulting in a pregnancy can be determined using binomial distribution f ( 1, 2, 0.1464) = 25%. That makes a pregnancy as likely as if it was a non-both WooHoo.

Edit 2: That method only works for simple pregnancy mode. I still have to come up with a general solution.

itch.io

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