The data set vitamin .txt contains the results of a study on vitamins. Three groups of test subjects each received a different treatment (three different vitamin formulations). Each subject's calcium levels before and after treat ment were recorded.
(a) To reduce bias in the experiment, the subjects should have been assigned a treatment regimen at random.
i. Explain what this means.
ii. Using just the "before" calcium levels, how could we check if any obvious non-random assignment was used?
iii. Perform this check, and comment on the results.
(b) Make separate scatter plots for the three sets of data.
(c) Write a report summarizing the experiment and its results.