An article in the American Industrial Hygiene Association Journal (Vol. 37, 1976, pp. 418€“422) describes a field test for detecting the presence of arsenic in urine samples.
The test has been proposed for use among forestry workers because of the increasing use of organic arsenics in that industry. The experiment compared the test as performed by both a trainee and an experienced trainer to an analysis at a remote laboratory. Four subjects were selected for testing and are considered as blocks. The response variable is arsenic content (in ppm) in the subject€™s urine. The data are as follows:

(a) Is there any difference in the arsenic test procedure?
(b) Analyze the residuals from this experiment.

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Subject 2 0.05 0.05 Test Trainee Trainer Lab 3 4 0.05 0.05 0.04 0.04 0.03 0.15 0.17 0.04 0.04 0.10