Newscientist.com ran the headline \"Breakfast Cereals Boost Chances of Conceivin
ID: 3262236 • Letter: N
Question
Newscientist.com ran the headline "Breakfast Cereals Boost Chances of Conceiving Boys, " based on an article which found that women who eat breakfast cereal before becoming pregnant are significantly more likely to conceive boys. The study used a significance level of alpha = 0.01. The researchers kept track of 133 foods, and for each food, tested whether there was a difference in the proportion conceiving boys between women who ate the food and women who didn't. Of all the foods, only breakfast cereal showed a significant difference. If none of the 133 foods actually have an effect on the gender of a conceived child, how many (if any) of the individual tests would you expect to show a significant result just by random chance? test(s) Mathews, F., Johnson, P.J., and Neil, A. (2008). "You are what your mother eats: evidence for maternal preconception diet influencing foetal sex in humans." Proceedings of the Royal Society B: Biological Sciences. 275: 1643, 1661-1668.Explanation / Answer
Solution
A significance of 0.01 => there is 1% chance that the the null hypothesis will be rejected when it is actually true. i.e., P(H0 is rejected when it is true) = 0.01. Or, to put it in a different, but meaning the same, way is: P(the test is significant when the null hypothesis is true) = 0.01.
In this case, H0 is: food mother takes has no impact on the gender of the child. So, given this, P(the test is significant) = 0.01 and hence out of 133 cases, expected number of cases where the test is significant even when the food mother takes has no impact on the gender of the child = 133 x 0.01 = 1.33 ANSWER