EXAMPLE 3.21 Do the Randomization for the Utility Company Experiment Using Random Digits

As we did in Example 3.20, we will illustrate the method by randomizing 12 residences to three treatments. For Step 1, we assign the 12 residences the following labels:

Compare these labels with the ones we used in Example 3.20. Here, we need the same number of digits for each label, so we put a zero as the first digit for the first nine labels.

For Step 2, we will use Table B starting at line 118. Here are the table entries for that line:

To make our work a little easier, we rewrite these digits in pairs:

We now select the labels for the first treatment, “Meter.” Reading pairs of digits from left to write and ignoring pairs that do not correspond to any of our labels, we see the labels 03, 04, 02, and 07. The corresponding residences will receive the “Meter” treatment. We will continue the process to find four labels to be assigned to the “Chart” treatment. We continue to the next line in Table B, where we do not find any labels between 01 and 12. On line 120, we have the label 04. This label has already been assigned to a treatment so we ignore it. Line121 has two labels between 01 and 12: 07, which has already been assigned to a treatment, and 10, which we assign to “Chart.” On the next line, we have 05, 09,and 08 which we also assign to “Chart.” The remaining four labels are assigned to the “Control” treatment. In summary, 02, 03, 04, and 07 are assigned to “Meter,”05, 08, 09, and 10 are assigned to “Chart,” and 01, 06, 11, and 12 are assigned to “Control.”