Lesson #13: can randomization really reduce Confounding ?

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.

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.

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).

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.

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?

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

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