Question

Dual-energy X-ray absorptiometry (DXA) is a technique for measuring bone health. One of the most common measures is total body bone mineral content (TBBMC). A highly skilled operator is required to take the measurements. Recently, a new DXA machine was purchased by a research lab, and two operators were trained to take the measurements. TBBMC for eight subjects was measured by both operators. The units are grams (g). A comparison of the means for the two operators provides a check on the training they received and allows us to determine if one of the operators is producing measurements that are consistently higher than the other. Here are the data.

	Subject
Operator	1	2	3	4	5	6	7	8
1	1.323	1.342	1.079	1.226	0.939	1.004	1.182	1.287
2	1.323	1.322	1.073	1.233	0.934	1.019	1.184	1.304

Use a significance test to examine the null hypothesis that the two operators have the same mean. Give the test statistic. (Round your answer to three decimal places.)

1) T=

2) Give the degree of freedom =

3) Give the P-value. (Round your answer to four decimal places.) =

4) The sample here is rather small, so we may not have much power to detect differences of interest. Use a 95% confidence interval to provide a range of differences that are compatible with these data. (Round your answers to four decimal places.)

=( , )

Answer 1

from above

1)T=-0.294

degree of freedom =n-1=7

p value=0.777 (try 0.778 if this comes wrong)

4)

95% confidence interval =-0.0113 ; 0.0088