EXAMPLE 10 A Randomized Comparative Experiment

A college decides to compare the progress of 25 students taught in the classroom with that of 25 students taught the same material online. They select which students will be taught online by taking a simple random sample of size 25 from the 50 available students. The remaining 25 students form the control group. They will receive classroom instruction. The result is a randomized comparative experiment with two groups. Figure 7.3 outlines the design in graphical form.

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Figure 7.3: Figure 7.3 The design of a randomized comparative experiment to compare online and classroom instruction.

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The selection procedure of randomly assigning students to groups is exactly the same as it is for sampling:

  • Step 1. Label the 50 students 01 to 50.
  • Step 2. Go to the table of random digits (Table 7.1, page 298) and read successive two-digit groups. Skip over two-digit groups greater than 50 since these values are not used as labels. Also skip over any duplicates. For example, if you begin at line 106 in Table 7.1, the first five students chosen are those labeled 41, 50, 13, 15, and 27.
  • Step 3. Stop when you have selected 25 labels. The students corresponding to these 25 labels form the online group.

If you prefer, you can skip Steps 2 and 3 and use technology as outlined in Spotlight 7.1 (page 300) to randomly select the 25 labels for the Treatment 1 group. Here is the output using a Ti-84 graphing calculator and the randintNoRep command to select the labels for the Treatment 1 group sample: