Question

A 90% confidence interval for the mean weight of newborn babies was found to be from 6.5 to 8.5 pounds. Select the best interpretation for this confidence interval. We are 90% confident that the mean weight of newborn babies in this sample is between 6.5 to 8.5 pounds. We are 90% confident that the mean weight of all newborn babies is between 6.5 and 8.5 pounds. We are confident that the mean weight of 90% of all newborn babies is between 6.5 and 8.5 pounds. We are 90% confident that the mean weight of all possible samples of newborn babies is between 6.5 and 8.5 pounds.

Answer 1

Answer: Choice B

We are 90% confident that the mean weight of all newborn babies is between 6.5 and 8.5 pounds.

Explanatiion:

The idea is that if we generate say 100 confidence intervals, then about 90 of them should capture the true population mean (mu) somewhere in them. Choice A is close to being true, but replace "sample" with "population" to make the statement fully correct.

We don't need a confidence interval to estimate a sample statistic. A confidence interval is used to estimate a population parameter. Choice C is a trick answer and a common misconception about confidence intervals. Choice D is a slight variation of choice A. These facts allow us to rule out choices A, C and D.