XX or XY Odds

Natural Gender Selection

Are the odds of having a boy or girl really 50% each time? What if you already have one boy or 2 or 3 boys? Is it really a 50% chance that you will have a girl next? Let’s look at the odds of having a boy or a girl, given that previous children are all of the opposite gender.

Odds of Having a Girl
The odds of having a girl seem decrease after having each boy, but only very slightly. Even after 3 boys, you are only 6.4% more likely to have a 4th boy than a girl.

If you have no children, then statistically, you have a 49% chance of having a girl first.

  • If you have one boy, the odds of having a girl as a second child are 50%.
  • If you have 2 boys, the odds of having a girl as a third child are 47.7%.
  • If you have 3 boys, the odds of having a girl as a fourth child are 43.6%.

Odds of Having a Boy
The odds of having a boy seem to increase after having girls, except after 2 girls, when a 3rd girl is more likely.

If you have no children, statistically, the odds of having a boy first are 51%.

  • If you have one girl, the odds of having a boy next are 54.5%.
  • If you have 2 girls, the odds of having a boy next are 46%.
  • If you have 3 girls, the odds of having a boy next are 52.7%.

 

Gender and Birth Order
Given the informationabove, it looks like you are slightly more likely to have a boy, regardless of previous children. This is probably due to the overall 51/49 boy/girl birth ratio. This ratio, interestingly, varies slightly with birth order; it isn’t consistent among first-borns, second-borns, etc.

  • With first born children,  51.0% are Boys.
  • With second born children, 52.2% are Boys.
  • With third born children, 48.6% are Boys.
  • With fourth born children, 50.8% are Boys.

Odds of Having an All Same-Gender Family

If there are roughly even odds of having a boy or a girl with each baby, given the laws of chance we should still expect to see some all same-gender families, even in large families. Here is the number of all same-gender families we would expect to see, using good ole fashioned statistics:

Family Size Same       -          Gender Mixed-Gender
2 Children 50% 50%
3 Children 25% 75%
4 Children 12.5% 87.5%
5 Children 6% 94%
6 Children 3% 97%
7 Children 1.6% 98.4%

Conclusion
Although we often hear from our moms, grandmothers even doctors that the chance for you to keep having the same gender, this is just an old wives tale. It is NOT a fact. The truth is, your odds stay pretty close to 50% for each child and only vary slightly. If you have had 2 or 3 boys, you are only about 2% to 6% more likely to have another boy. If you have had girls, you are slightly more likely to have a boy next.

Data taken from Chance Magazine article 2001 and ingender.com

Related posts:

  1. Children Born From Frozen Embryos Weigh More And Do Better Than Those Born After Fresh Transfer
  2. The Science of Gender Swaying

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