Periodontal disease may play a role in many diseases, some of which were unknown previously. For example, a recent study of the failure of joint replacement prostheses due to aseptic loosening demonstrated a link with bacterial DNA that was also found in dental plaque. Therefore, it is crucial that methods of determining bacterial DNA in plaque have a high degree of ­reliability. A study was conducted to examine the variability in the chemical analyses for specified bacterial DNA content in plaque. The two major sources of variation selected for investigation were the person con-ducting the analysis and the subjects supplying the plaque. The researchers randomly selected five analysts from a large pool of experienced analysts and 10 female subjects (ages 18€“ 20). Plaque was scraped from the entire dentition of each subject and divided into five samples. Each of the analysts was given an unmarked sample from each of the subjects. The analysts then made a determination of the DNA content (in micrograms) for each of the 10 samples. The data are given here.

a. Why do you think the researchers selected only female subjects who were essentially the same age?
b. Write an appropriate linear statistical model identifying all terms in the model.
c. State the null and alternative hypotheses for testing for an effect due to analyst.

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Subject Analyst 1 10 9.9 106 115 113 10.5 8.0 106 122 8.0 9.7 10.2 10.6 113 116 10.3 8.2 10.7 12.8 79 9.6 10.2 10.5 11.2 113 10.2 7.9 10.5 12.7 78 9.4 10.4 109 114 11.6 10.6 8.4 10.9 12.5 8.1 9.5