FA. The Johnsons

 We ask an old chestnut on the second Math Factor segment ever aired, from February 1, 2004: The Johnsons have two children; we’re told one is a boy. What is the probability they have two boys?


(Incidentally, the music is R. Crumb’s band, Les Primitifs Du Futur)

1 Comment »

  1. jlundell said,

    March 8, 2009 at 11:07 pm

    I was reading the last but one issue of Science (27 Feb) and came across an article Making Every Baby Girl Count (p1164). You may need a subscription, so I’ll quote a bit of the article below. The context is that the sex ratio at birth in China these days is 120 boys for every 100 girls, related to a cultural preference for sons. The ratio has climbed over the years, presumably due to technology (ultrasound in particular).

    It’s a long and interesting article on research into the problem and measures the government is taking to get back into balance, but the piece that relates to tMF is:

    “In 1980, China, concerned about a population explosion, adopted a one-child policy– and enforced it through compulsory sterilizations and abortions. The policy clashed with the country’s patrilineal tradition, in which sons carry on the ancestral line and care for elderly parents. Many families went to great lengths to ensure that their sole child was a boy. Confronted with a spike in the sex ratio and widespread resistance to coercive methods, Communist Party leaders relaxed the one-child policy in 1984. Most provinces subsequently allowed rural couples with one girl to try again, an exception sometimes termed the ‘1.5-child policy.’ But the change coincided with the introduction of ultrasound machines to rural China, which enabled couples to determine the sex of a fetus and abort females. The country’s sex ratio continued to rise.”

    The “1.5-child policy” wouldn’t in itself change the ratio, of course, at least not on the basis of statistics. It would, however, increase the number of families with at least one boy.

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