1. Day 31 AGENDA:
DG minutes
Hand back THQ3

2. Advanced Placement Statistics
Section 5.2: Designing Experiments (Part II)
EQ: What is blocking and how is it used in experimental design?

3. Terms to Recall: Ex. Identify the experimental unit and
treatment for each.
A cornfield is divided into 4 parts, each part treated with a different fertilizer.
Experimental Unit is the cornfield. Treatment is the fertilizer.

4. Terms to Recall: Ex. Identify the experimental unit and
treatment for each.
2. A teacher practices different teaching methods on different groups of students in her class to see which yields the best results.
Experimental Units are students in the teacher’s class. The treatment is the teaching methods.

5. Terms to Recall: Ex. Identify the experimental unit and
treatment for each.
3. A doctor treats a patient with a skin condition with different creams to see which is most effective.
Experimental Unit is the patient. The treatment is the cream.

6. Ex. Identify the experimental units, treatment, factor, and level for each.
4. Runners were randomly assigned to groups in an experiment to determine how well a drug helped relieve muscle ache. Groups were randomly assigned the drug in either a 5mg, 10mg, or 15 mg dosage.
Experimental Units are the runners. The treatment is the drug. The factor is the dosage. The levels of dosage of the drug are 5 mg, 10mg, and 15 mg.

7. Ex. Identify the experimental units, treatment, factor, and level for each.
5. Mice were randomly assigned to groups in an experiment to determine how well a lotion stimulated hair growth. Groups were randomly assigned to receive one of three lotions, A, B, and C.
Experimental Units are the mice. The treatment is the lotion. The factor is the type of lotion. The levels are lotion type A, lotion type B, and lotion type C.

8. Ex. Identify the experimental units, treatment, factor, and level for each.
6. Runners are randomly assigned to three different groups and are randomly assigned to receive three different training methods.
Experimental Units are the runners. The treatment is the training. The factor is the method of training. The levels are training method 1, training method 2, and training method 3.

9. Ex. Does regularly taking aspirin help protect people against heart attacks? The Physicians Health Study looked at the affects of two drugs: aspirin and beta carotene. Their medical study involved 21,996 male physicians.
Beta Carotene
YES NO
Aspirin
ASP/BC
ASP/PLACEBO
YES NO
PLACEBO/BC
PLACEBO/PLACEBO
Aspirin
Beta Carotene
Placebo
Type of Drug
All people
Male physicians 4

10. Ex. Researchers are studying the absorption of a drug into the bloodstream. A drug is injected into 25 people. The concentration of the drug in the bloodstream is measured 30 minutes after the injection.
25 subjects
amt of time drug is in the bloodstream
Concentration of drug in bloodstream
1 drug
1 dosage level of the drug
1 treatment

11. Ex. Researchers are studying the absorption of a drug into the bloodstream. A drug is injected into 25 people. The concentration of the drug in the bloodstream is measured 30 minutes after the injection.
1 drug
3 dosage levels
3 treatments

12. Assignment:
p #33, 35, 37
p #

13. RECALL: In Sampling Design: Strata Samples In Experimental Design:
Blocking
Experiments

14. Types of Design:
1. Completely Randomized Design --- subjects are assigned to treatments completely at random.

15. Ex. In an education study, students from several classrooms are randomly assigned to one of four treatment groups (three new types of a test and the standard). The total number of students in 4 classrooms is 96. Randomly assign 1/4 of them, or 24 students, to each of the 4 types of tests. The treatments are the tests. The primary interest is the main effect of the test.

16. Randomized Complete Block Design --- subjects are divided into blocks according to some homogeneous characteristic within that block . Subjects in each block are then randomly assigned to treatments so that all treatment levels appear in each block.
“Matched Pairs” --- pair units by height, race, age, gender, income, etc.; each unit serves as a block; each unit receives ALL treatment
NOTE: Matched Pairs can occur in both
experiments and observational studies.

17. Blocking Design:
Blocks are groups of experimental units that are formed to be as homogeneous as possible with respect to the block characteristics. The term
block comes from the agricultural heritage of experimental design where a large block of land
was selected for the various treatments.

18. The blocks of land had uniform soil, drainage, sunlight, and other important physical characteristics. Homogeneous clusters improve the comparison of treatments by randomly allocating levels of the treatments within each block.

19. Blocking helps reduce the effects of lurking variables, but will not eliminate them.
You must give a reason for your blocking method.
Ex. Block subjects by gender because drug affects males and females in different ways
Ex. Block plants with respect to sunlight because of effect of light on growth.

20. NOTE: YOU DON’T “RANDOMLY ALLOCATE”
SOMEONE INTO A BLOCK.

22. KEYS to Blocking Design:
collect experimental units on a key similar variable; must be justified
identify “block” before beginning experiment
randomly assign treatments within blocks

23. Controls KNOWN variables Controls UNKNOWN variables
Blocking vs Randomization
Controls KNOWN
variables
Controls UNKNOWN
variables

24. Blind Study: Double Blind Study:
Subjects don’t know which group they have been assigned to --- primary treatment or control group
Double Blind Study:
Both the subjects and the data collectors are blind to the treatment information.

26. a) What is the treatment in this experiment?
Ex. Women and men respond differently to advertising. An experiment to compare the effectiveness of three commercials for the same product will want to look at the reactions of men and women separately, as well as the overall response to the ads.
a) What is the treatment in this experiment?
What is the factor of the treatment?
c) What is/are the levels?
The treatment in this experiment is advertising.
The factor in this experiment is commercials.
The levels in this experiment are the 3 different commercials.

27. Ex. Women and men respond differently to advertising
Ex. Women and men respond differently to advertising. An experiment to compare the effectiveness of three commercials for the same product will want to look at the reactions of men and women separately, as well as the overall response to the ads.
d) A completely randomized design considers all subjects, both men and women, as a single pool. This ignores the differences between men and women. Describe a design for this experiment.

28. Alphabetize the men and women into a single list
Alphabetize the men and women into a single list. Assign digits to each member of the list.
Use a random digit table reading ?- digit numbers at the time, to randomly assign “x” subjects to the first group (watching commercial 1). Then randomly assign “x” subjects to the second group (watching commercial 2). The remaining subjects will be place in the third group ( watching commercial 3). Repetition is not allowed since the numbers represent a unique person.
Compare effectiveness of commercials by comparing reactions of the three groups.

29. Subjects Random Allocation Group 1 (Watch Commercial 1) Group 2
Compare
Reactions
of Groups to Determine Effectiveness of Commercials
Group 2
(Watch Commercial 2)
Subjects
Random
Allocation
Group 3
(Watch Commercial 3)

30. Ex. Women and men respond differently to advertising
Ex. Women and men respond differently to advertising. An experiment to compare the effectiveness of three commercials for the same product will want to look at the reactions of men and women separately, as well as the overall response to the ads.
e) A block design considers men and women separately. Randomly assign women to three groups, then randomly assign men to three groups. Describe a design for this experiment.

31. Since women and men may react differently to the same commercial, block subjects by gender. Alphabetize men and women in their respective blocks. Assign digits to subjects in each block.
Use a random digit table reading ?-digit numbers at the time, to randomly assign “x” females to the first female group (watching commercial 1). Then assign “x” females to the second female group (watching commercial 2). The remaining females will be place in the third group
(watching commercial 3). Repeat this process for the males.
Repetition is not allowed within either block since the
numbers represent a unique person.
Compare effectiveness of commercials on gender by comparing reactions within each block. Compare reaction results of women to men.

32. Males Block by Gender Females Group 1 Commercial 1 Group 2
Compare
Reactions
of Groups to Determine Effectiveness of Commercials on Males
Group 2
Commercial 2
Males
Random
Allocation
Group 3
Commercial 3
Compare
Reactions
of Genders to Determine Effectiveness of Commercials
Subjects
Group 1
Commercial 1
Block by Gender
Compare
Reactions
of Groups to Determine Effectiveness of Commercials on Females
Group 2
Commercial 2
Females
Random
Allocation
Group 3
Commercial 3

33. Assignment:
p #45 – 48