chap. 5 sec. 2a notes.pptx

8/14/2019 Chap. 5 Sec. 2a Notes.pptx

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Designing ExperimentsChapter 5 Section 1a


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Variables

Response The variable we are studying

by the outcome of an

experiment Also called dependent variable

Explanatory Helps explain or influences

changes in the response variable

Also called independent variable


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Basic Vocab of Experiments Experimental Units

The individuals on which the experiment is done Called SUBJECTS if the units are humans

Factors The explanatory variables of an experimentTreatment

The specific experimental condition applied to the units


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#5.34 Identify the experimental units, factors,treatments, and the response variables You can use your computer to make long-

distance telephone calls over the Internet. How will the cost affect the use of this service? Auniversity plans an experiment to find out. It will offer the service to all 350 students in one ofits dormitories. Some students will pay a low

flat rate. Others will pay higher rates at peakperiods and very low rates off-peak. Theuniversity is interested in the amount and timeof use and in the effect on the congestion of the

network.


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More Vocab (Ex. 5.15 pg. 356) Basic design of a single treatment experiment

Treatment Observe Response Placebo Effect

When a dummy treatment is as effective as theactual treatment

This is caused by outside factors

Control Group A group of experimental units that receive aplacebo or no treatment, but experience thesame conditions as the treatment group


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Basic Principles of Statistical Design ofExperiments1. Control2. Replication3. Randomization


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Control The overall effort to minimize the effects of

lurking variables on the response (Dont confuse w/ Control Group)

Comparison is the simplest form of control. Compare two or more treatments (Control Group

& Treatment Group) in order to preventconfounding the effect of a treatment with otherinfluences, such as lurking variables.

Think Gastric Freezing Example (pg. 358) Uncontrolled experiments usually show a much

higher success rate than proper comparative

experiments


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Replication Use enough subjects to reduce (it cannot

eliminate) chance variation & bias This DOES NOT mean repeat the same

experiment a 2 nd time in this instance. Would you expect to get the exact same results if

you did?


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Randomization Use impersonal chance (probability) to assign

experimental units to treatments. Systematic differences among groups of

experimental units in a comparative experimentcause biaschance (probability) eliminates this!

Randomization allows us to assume that thetreatment groups are essentially similar.


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Diagramming Experiments

#5.44 on page 366What to show: randomization, size of groups, treatments,response variable


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Statistical Significance An observed effect

so large that it would rarely occur by chance.

Think back to

Gastric FreezingExample (pg. 356)


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Pg. 357 5.33-5.37 oddPg. 364 5.39-5.43 oddHomework Assignment

Read pages 358-371

chap. 5 sec. 2a notes.pptx

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