Question

1. Listed below are amounts of strontium-90 (in millibecquerels per gram of calcium) in a simple random sample of baby teeth obtained from Pennsylvania residents and New York residents born after 1979. (based on data from “An Unexpected Rise in Strontium-90 in U.S. Deciduous Teeth in the 1990’s, Science of the Total Environment, Vol 317)

Penn: 155            142         149         130         151         163         151         142         156         133         138         161

NY:         133        140         142         131         134         129         128         140         140         140         137         143

1. Construct a 95% confidence interval for the difference in the means – you decide on which population is population 1 and which is population 2
2. Does the confidence interval give credence to the claim that the average amount of Strontium -90 in teeth from Penn is greater than that from NY. Explain completely

Answer 1

a)

t value at 95% = 2.2010

CI = (x1 -x2) +/- t *sqrt(s1^2/n1+s2^2/n2)
= (147.5833 - 136.4167) +/- 2.2010 * sqrt(10.6383^2/12 + 5.2129^2/12)
= (3.6395,18.6938)

The 95% CI is (3.6395,18.6938)

b)

yes, because confidence interval does not contain the hypothesized value i.e.0