It is suspected that American women are now waiting longer tohave their first ba

Question

It is suspected that American women are now waiting longer tohave their first baby than they did a decade ago. The hypothesis isto be tested by selecting the first 10 women on an alphabeticallist of women who have had babies at a local hospital in the lastyear. The mean age of this sample will be examined to see if themean age at which they had their first child has increased duringthe past 10 years. The sample values are: 31, 27, 30, 32, 27, 27,27, 27, 21, 24. Decide whether or not the conditions andassumptions for inference with a t-test are satisfied. A) This is not a random sample. B) The conditions and assumptions are satisfied. C) 10 women is more than 10% of the poption of women who havehad babies at the local hospital. D) The sample does not seem to come from a normalpopulation. E) The sample size must be at least 30 to use a t-test. It is suspected that American women are now waiting longer tohave their first baby than they did a decade ago. The hypothesis isto be tested by selecting the first 10 women on an alphabeticallist of women who have had babies at a local hospital in the lastyear. The mean age of this sample will be examined to see if themean age at which they had their first child has increased duringthe past 10 years. The sample values are: 31, 27, 30, 32, 27, 27,27, 27, 21, 24. Decide whether or not the conditions andassumptions for inference with a t-test are satisfied. A) This is not a random sample. B) The conditions and assumptions are satisfied. C) 10 women is more than 10% of the poption of women who havehad babies at the local hospital. D) The sample does not seem to come from a normalpopulation. E) The sample size must be at least 30 to use a t-test.

Explanation / Answer

I would say that the answer is A: this isnot a random sample; because the sample was thefirst 10 women on the alphabetical list, perhaps there arepeople related to each other with the same last name starting withA or B or C or whatever, and they may have similar waiting times(and so the sample would not be random); a betterway to pick the sample would be to assign each person a number andpick 10 numbers randomly. It is posible that name and waiting timeare independent, so the sample would be random, but there is no wayto tell, so you're safer with just picking 10 random numbers or 10out of a hat.

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