Homework: pg. 357 #34-36, 38 34.) Subjects: the students living in the selected dormitory Factor: the rate structure Treatments: paying one flat rate or paying peak/off-peak rates Response: the amount and time of use and total network use 35.) Subjects: the individuals who were called Factors: (1) type of call; (2) offered survey results Treatments: (1) giving name/no survey results; (2) identifying university/ no survey results; (3) giving name and university/ no survey results; (4) giving name/offering survey results; (5) identifying university/offer survey results; (6) giving name and university/offering survey results Response: whether or not the interview was completed

36.) Subjects: 300 sickle-cell patients Factor: type of medication Treatments: hydroxyurea and placebo Response: number of pain episodes 38.) A. Units: middle schools Response: physical activity and lunchtime consumption of fat B. There are two factors (physical activity program and nutrition program) and four treatments (activity intervention, nutrition intervention, both interventions, and neither intervention). C. At least four experimental units are required for the experiment; but, as we will see in the next section, using only four experimental units is not a good idea.

5.2 Principles of Experimental Design

Experimental Design Basic Principles of statistical design of experiments: Control the effects of lurking variables on the response (compare 2 or more treatments) Replicate each treatment on many units to reduce chance of variation in the results Randomize—use impersonal chance to assign experimental units to treatments

Sit or Stand Activity: Control: Replicate: Randomize:

Experimental Design Completely randomized design—all units are assigned a treatment at random

Example: pg. 364 #39 You are trying to compare the effectiveness of two ways to treat prostate disease. The two treatments are traditional surgery and a new method that does not require surgery. You have 300 prostate patients who are willing to serve as subjects in an experiment. Use a diagram to outline the design of a randomized comparative experiment.

Experimental Design (Form of Control) Block design —group of units that are known to be similar before the treatments Form blocks based on most important, unavoidable sources of variability Then randomly assign treatments within each block EACH block should have units that receive each treatment Blocks ≠ Treatment groups For example, block design is necessary if you have 50 female and 20 male volunteers to use in a medication study, and you think that the medication might affect men and women differently. Form blocks by gender by putting the 50 females on one list and the 20 males on another. Randomly choose 25 females and 10 males to be in the treatment group. The remaining 25 females and 10 males will be the control group. Since both groups have the same gender makeup, any difference between the groups can be attributed to the medicine, not to gender differences.

Experimental Design Matched Pairs design —block 2 units together based on similar traits Randomly assign treatments (one control; one treatment) Can be a match with yourself Common Block Design

Pg. 372 #48 We want to compare the growth of trees given more CO2 and those that were not. We can afford to treat 3 circular areas with more CO2 A.) Describe a completely randomized design using 6 well separated 30 meter circular areas in a pine forest. B.) Areas within the forest may differ in soil fertility. Describe a matched pairs design using three pairs of circles that will reduce the extra variation due to different fertility. Sketch the circles and carry out the randomization your design calls for.

Double blind experiment —neither subjects nor those who measure the response variable know which treatment a subject received Helps treat every subject the same, regardless of treatment Lack of realism —cannot realistically duplicate conditions we want to study

Goal of experiments: Statistically Significant: an observed effect so large that it would rarely occur by chance Review of 5.2 is on page 373. Good overview of new vocabulary.

HW: pg 365 #41, 44 pg 371 #49,50