Unfortunately, that vague estimate is as precise as we can be. Now we turn to 4 factors that influence how much risk comes from your side of the family. You can apply these same factors to members of your partner's family as well to try to be more precise than the broad estimate given in step 1 above. It looks like the earlier a person has symptoms, the more likely they are to transmit the illness. There are other illnesses which seem to work like this as well.
Stress seems to make bipolar symptoms emerge.
Researchers don't know for sure, but it looks like it may have quite an impact, changing the risk quite a bit. This simply means that if you are pretty young, you are in a generation that's been shown in other research to have a higher likelihood of having bipolar disorder. That's because the illness itself seems to be getting more common. By comparison with factor B above, this factor is much smaller. Yes, there is a lot of guessing about why this occurs as well.