Human beta-endorphin (HBE) is a hormone secreted by the pituitary gland under conditions of stress. A researcher conducted a study to investigate whether a program of regular exercise might affect the resting (unstressed) concentration of HBE in the blood. He measured blood HBE levels, in January and again in May, from 10 participants in a physical fitness program. The results were as shown in the table.14
(a) Construct a 95% confidence interval for the population mean difference in HBE levels between January and May

(b) Interpret the confidence interval from part (a). That is, explain what the interval tells you about HBE levels. (See Examples 6.3.4 and 6.3.5.)
(c) Using your interval to support your answer, is there evidence that HBE levels are lower in May than January?

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HBE Level (pgml) Participant ny May Differenc Mean 378