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DRILL

DRILL. If you needed to select 5 students from a group of 2250, how could you use the table of random digits to carry out the selection process. Starting at line 118 what are the numbers of the five students. Section 5.2 Designing Experiments. AP Statistics November 9, 2010. Terminology.

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DRILL

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  1. DRILL • If you needed to select 5 students from a group of 2250, how could you use the table of random digits to carry out the selection process. • Starting at line 118 what are the numbers of the five students.

  2. Section 5.2Designing Experiments AP Statistics November 9, 2010

  3. Terminology • The individuals on which the experiment is done are the experimental units. • When the units are human beings, they are called subjects. • A specific experimental condition applied to the units is called the treatment.

  4. Experiments Units Treatment Observe Response

  5. More terminology • The explanatory variables in an experiment are often called factors. • Each treatment is formed by combining a specific value (often called a level) of each of the factors.

  6. Comparative Experiments • When first conducting an experiment you first must state the explanatory and response variables. • Treatment  Observation • Observation 1  Treatment  Observation 2

  7. The Physicians’ Health Study Does regularly taking aspirin help protect people against heart attacks? The Physicians’ Health Study looked at the effects of two drugs: aspirin and beta carotene. The body converts beta carotene into vitamin A, which may help prevent some forms of cancer. A combination of the drugs were given 21,996 male physicians.

  8. The Physicians’ Health Study • Subjects? • Physicians • Treatments? • 4 (the groups-> • Factors? • 2 (aspirin & beta carotene)

  9. The Placebo Effect “Gastric freezing” is a clever treatment for ulcers in the upper intestine. The patient swallow a deflated balloon with tubes attached, the a refrigerated liquid is pumped through the balloon for an hour. The idea is that cooling the stomach will reduce its production of acid and so relieve ulcers. An experiment reported in the Journal of the American Medical Association showed that gastric freezing did reduce the acid production of and relieve ulcer pain.

  10. The Placebo Effect The “Gastric freezing” experiment was poorly designed. The patients’ response may have been due the placebo effect. A placebo is a dummy treatment. Many patients respond favorably to any treatment, even a placebo. This may be due to trust in the doctor and expectations of a cure, or simply to the fact that medical conditions often improve without treatment.

  11. Groups in an Experiment • Sometimes a group will be used in an experiment, where they think they are receiving a treatment but they are really receiving a placebo. This group is called the control group. • The control group may also be a group they is not receiving the treatment. • People who receive the “real” treatment are the treatment group.

  12. Group 1 Aspirin/Beta Carotene Group 2 Aspirin/Placebo Group 3 Placebo/Beta Carotene Group 4 Placebo/Placebo Experiments Compare Response Units

  13. Principles of Experimental Design • Control of effects of lurking variables on the response, most simply by comparing several treatments. • Randomization, the use of impersonal chance to assign subjects to treatments. • Replication of the experiments on many subjects to reduce chance variation in the results.

  14. Statistical Significance • An observed effect so large that it would rarely occur by chance is called statistically significant.

  15. Double-Blind Experiment • In a double-blind experiment neither the subject or the person in contact with them knows which treatment a subject received if any.

  16. Experiments without placebos • Matched pair design • In a matched pair design, subjects are paired by matching common important attributes. • Often the results are a pre-test and post-test with the unit being “matched” to itself.

  17. Block Design • A block design is a group of experimental units or subjects that are similar in ways that are expected to affect the response to the treatments. • In a block design, the random assignment of units to treatments is carried out separately within each block.

  18. Groups in an Experiment • Sometimes in experiment they will use matching to create the groups of individuals. • Matching is when you try to match the two groups up so that they have the same number of people in different categories such as age, sex, race, etc…

  19. Matching • When matching is combined with a block design you create a matched-pairs design. • Each block would consist of two people who each have similar traits. One would get the treatment

  20. Classwork/Homework • PAGES 284 – 285 #’s 5.46, 5.47, 5.49, 5.52, 5.53

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