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You may have heard it from your know-it-all in-law, or a snidely friend who happens to have one-of-each, or maybe even your doctor: after having 2 or 3 boys, you might as well forget about ever having a daughter, because the odds are you're going to keep having boys. Or if you've only had girls, maybe you "just can't make" a boy. Well, think again. Remember that looking at very small data samples (two or three children) is very misleading: so let's take a look at data for over 6,000 American families, and find out:
The 51/49 Boy/Girl Ratio
The ratio of 51% boys to 49% girls seen here is representative of overall US birth rates. There are many hypotheses about why there are slightly more boys born each year than girls, but no one knows for sure why this is so. Here are a couple of the theories:
Regardless of the reason, the 51/49 ratio remains constant year to year throughout the US population. Are Boys or Girls Preferred?Do parents tend to keep having children in hopes of having a boy or a girl? In some cultures, there is a strong desire for a son, but parents in the US may have a "balance preference", a desire to have one of each gender. Here's what the data shows: Did the first child's gender influence whether to have a second child?
Did previous children's gender influence whether to have a third child?
Combining boy/boy and girl/girl, we see:
What about the fourth child?
Combining this into same-gender and mixed-gender families, it turns out they are almost equally likely to have a 4th child, although same-gender families are slightly more likely.
The Odds of Having a Another Boy or GirlOkay, finally! 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 After 1, 2, or 3 BoysThe 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.
Odds of Having a Boy After 1, 2, or 3 GirlsThe odds of having a boy seem to increase after having girls, except after 2 girls, when a 3rd girl is more likely.
Gender and Birth OrderGiven the data above, 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.
What's it all mean?Although we often hear the "statistic" that you are 30% or even 70% more likely 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 very slightly more likely to have another boy. If you have had girls, you are slightly more likely to have a boy next. Don't believe that you can "only make" boys or girls -- most likely, it's only chance! You'll also want to see: What are the odds of having all boys or all girls? |