1. Aim: How do we randomize?

2. How to randomize The idea of randomization is to assign subjects to treatments by drawing names from a hat. In practice, experimenters use software to carry out randomization. – Simple Random Sample You can randomize without software by using a table of random digits

3. Table of Random Digits A table of random digits is a list of the digits 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 that has the following properties: 1.The digit in any position in the list has the same chance of being any one of 0, 1, 2, 3, 4, 5, 6, 7, 8, 9. 2.The digits in different positions are independent in the sense that the value of one has no influence on the value of any other.

4. What does the numbers of the table mean? Table B begins with the digits 19223950340575628713. To make the table easier to read, the digits appear in groups of five and in numbered rows. The groups and rows have no meaning Our goal is to use random digits for experimental randomization.

5. The facts about random digits Any pair of random digits has the same chance of being any of the 100 possible pairs: 00, 01, 02, …, 98, 99. Any triple of random digits has the same chance of being any of the 1000 possible triples: 000, 001, 002, …, 998, 999. … and so on for groups of four or more random digits.

6. Example: Cell Phones Does talking on a hands-free cell phone distract drivers? Undergraduate students “drove” in a high-fidelity driving simulator equipped with a hands-free cell phone. The car ahead brakes: how quickly does the subject respond? Twenty students (the control group) simply drove. Another 20 (the experimental group) talked on the cell phone while driving. This experiment has a single factor (cell phone use) with two levels. The researchers must divide the 40 student subjects into two groups of 20. To do this in a completely unbiased fashion, put the names of the 40 students in a hat, mix them up, and draw 20. These students form the experimental group and the remaining 20 make up the control group.

7. Example: Cell Phones In the cell phone example, we must divide 40 students at random into two groups of 20 students each. Step 1: Label. Give each student a numerical label, using as few digits as possible. Two digits are needed to label 40 students, so we use labels - It is also correct to use labels 00 to 39 or some other choice of 40 two-digit labels. Step 2: Table. Start anywhere in Table B and read two- digit groups. Suppose we begin at line 130, which is The first 10 two-digit groups in this line are