A group of sheep, infested with tapeworms, are randomly divided into two groups as follows. Each sheep is assigned a number (1 through 20) and then 10 numbers are selected by drawing 10 slips of paper from a box having the numbers 1 through 20written on them. The drawing divides the sheep into two groups. One group is given a placebo and the other is given an experimental drug. After six weeks the sheep are sacrificed and tapeworm counts are made. Do these samples represent dependent or independent samples?
Sol: Here, the samples are independent. We are working with subjects (sheep) and have randomly selected a group of 20 infected sheep and divided this group into two. So, we can make inference about the population, i.e., the effect of the drug on sheep based on the results of the two groups. Also, the samples of placebo group are by no means dependent on the group of experimental drug. Therefore, the tapeworm counts of one group do not affect the other. All these observations lead us to conclude that the two samples are indeed independent.
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