AP Stats Name______
Chapter 12
Vocabulary
Observational study
Retrospective study
Prospective study
Experiment
Random assignment
Factor
Response
Experimental units
Level
Treatment
Principles of experimental design
Control
Randomize
Replicate
Block
Statistically significant
Control group
Blinding
Single blind
Double blind
Placebo
Placebo effect
Block
Matching
Designs
Confounding
Examples: Study or Experiment?
The leg muscles of men aged 60 to 75 were 50% to 80% stronger after they participated in a 16 week, high intensity resistance-training program twice a week. (Journal of Gerontology 55A, 2000)
Among a group of disabled women aged 65 and older who were tracked for several years, those who had a vitamin B12 deficiency were twice as likely to suffer severe depression as those who did not. (American Journal of Psychology 157, 2000)
To research the effects of “dietary patterns” on blood pressure in 459 subject, subjects were randomly assigned to three groups and had their meals prepared by dieticians. Those who were fed a diet low in fat and cholesterol and high in fruits, vegetable, and low-fat dairy foods (known as the DASH diet) lowered their systolic blood pressure by an average of 6.7 points when compared with subjects fed a control diet.
Example 2:
A farm-product manufacturer wants to determine if the yield of a crop is different when the soil is treated with three different types of fertilizers. Fifteen similar plots of land are planted with the same type of seed but are fertilized differently. At the end of the growing season, the mean yield from the sample plots is compared.
Experimental units?
Factors?
Levels?
Response variable?
How many treatments?
Example 3:
A consumer group wants to test cake pans to see which works the best (bakes evenly). It will test aluminum, glass, and plastic pans in both gas and electric ovens.
Experiment units?
Factors?
Levels?
Response variable?
Number of treatments?
Example 4:
A farm-product manufacturer wants to determine if the yield of a crop is different when the soil is treated with three different types of fertilizers. Fifteen similar plots of land are planted with the same type of seed but are fertilized differently. At the end of the growing season, the mean yield from the sample plots is compared.
Why is the same type of seed used on all 15 plots?
What are other potential extraneous variables?
Does this experiment have a placebo? Explain
Example 5:
An article from USA Today reports the number of victims of violent crimes per 1000 people. 51 victims have never been married, 42 are divorced or separated, 13 are married, and 8 are widowed.
Is this an experiment? Why or why not?
What is a potential confounding variable?
Example 6:
Four new word-processing programs are to be compared by measuring the speed with which standard tasks can be completed. One hundred volunteers are randomly assigned to one of the four programs and their speeds are measured.
Is this an experiment? Why or why not?
What type of design is this?
Factors? Levels?
Response variable?
Example 7:
Four new word-processing programs are to be compared by measuring the speed with which standard tasks can be completed. One hundred volunteers are randomly designed to one of the four programs and their speeds are measured.
Is there a potential confounding variable?
Example 8:
Suppose that the manufacturer wants to test a new fertilizer against the current one on the market. Ten 2-acre plots of land scattered throughout the county are used. Each plot is subdivided into two subplots, one of which is treated with the current fertilizer, and the other with the new fertilizer. Wheat is planted and the crop yields are measured.
What type of design is this? Why use this method?
When does randomization occur?