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Thread: Gender and birth year

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    Gender and birth year




    Okay this is probably simple but I'm wanting to verify. A co-worker's wife is pregnant with their 8th baby (yeah. It's a lot) and we are all betting on if it will be a boy or girl. The thing is, of their seven, all the girls (4) were born in even years and all the boys (3) in odd years. I know the probability of it being either one is 50/50 but is it less likely to continue the same pattern having defied the odds with the existing pattern already? What is the probibilty that this baby being born in 2016 will be a girl? Is it still 50/50 or do we take the improbility of the pattern into account?

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    Re: Gender and birth year

    Since it is still largely unknown what all of the factors are that determine birth gender, the usual 50:50 assumption is a reflection of those unknowns that make gender random for all practical purposes. The association between odd/even birth years and gender is in all likelihood a coincidence (what causal mechanism would possibly explain this observation?), and very probably says a great deal more about people’s propensity for looking for patterns than about the mechanics of birth gender, besides illustrating the danger of drawing conclusions from very small data sets.

    Moreover, there is no known mechanism that makes the latest birth gender dependent on a mother’s prior offspring history. In fact, there is much empirical evidence to suggest that successive birth genders are effectively independent events, much like successive flips of a coin are.

    In short, bet that it’s a boy since there are slightly more of them born worldwide.

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    Re: Gender and birth year


    That makes sense. So in this situation the improbability of the extraordinary pattern continuing is not taken into account? Obviously it is less probable that the pattern will continue on 8 of 8 times than it did 7 of 7 times (like rolling dice (one for gender and one for year.. odd representing male and odd year & even representing female and even year)... with the dice, the more you role the less likely you will adhere to the pattern. This isn't the case with a individual birth taken on its own because the odds are slightly above 50/50. Is that right?

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