1. Lesson #13: can randomization really reduce Confounding ?

2. Consider this scenario…
To demonstrate how randomization reduces confounding, a nutrition experimenter intends to compare the weight gain of newly weaned male rats fed Diet A with that of rats fed Diet B.
To do this, she will feed a diet to 10 rats. She has available 10 rats of genetic strain 1 and 10 rats of genetic strain 2.

3. Continued…
Strain 1 is more vigorous, so if the 10 rats of strain 1 were fed Diet A, the effects of strain 1 and Diet A would be confounded and the experiment would be biased in favor of Diet A.

4. Group Work (will be turned in)
Label the rats 00, 01, …, 19.
Use Table A to assign 10 rats to Diet A. (The first 10 valid non-duplicate numbers found will be assigned to Diet A; those remaining will be assigned to Diet B).

5. Next… Take your results and record them on the board as follows:
Table ___
Group # 1:
List the 10 rat numbers which you have chosen for Diet A based upon the Table.

6. Now…
Unknown to the experimenter, the rats labeled 00, 02, 04, 06, 08, 10, 12, 14, 16, and 18 are the 10 strain 1 rats.
How many of these rats were in the Diet A group that you generated?
What was the average number of strain 1 rats assigned to Diet A for the class?

7. Finally…
Write a statement regarding your findings with randomization and its effects on confounding in experiments.

8. Don’t forget… The 3.1 Quiz is scheduled for Wednesday (Period 5)
Thursday (Period 2 and 6)