Designing Experiments

An SRS is a...

• Simple random sample where each element of the population has the same chance of being selected

• Simple random sample where the some elements in the population are more likely to be chosen than others.

• Stratified random sample where each element of the population has an equal chance of being selected

• Systematic random sample where each element of the population has an equal chance of being selected

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A recent study showed that tea drinkers have lower stress levels than coffee drinkers. Tea drinkers are known to have a higher proportion of yoga practitioners than coffee drinkers, and they exercise on average two hours per week more than their coffee-drinking counterparts. What is the term used to describe these additional factors that might have an effect on the stress levels of tea drinkers?

• cause and effect variables
• confounding variables
• sampling variables
• unfounded variables

Which of the following is a true statement?

• A) While properly designed experiments can strongly suggest cause-and-effect relationships, a complete census is the only way of establishing such a relationship.

• B) If properly designed, observational studies can establish cause-and-effect relationships just as strongly as properly designed experiments.

• C) Controlled experiments are often undertaken later to establish cause-and-effect relationships first suggessted by observational studies.

• D) A useful approach to overcome bias in observational studies is to increase the sample size.

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The question about the theme for prom is posed during the morning announcements. Students are asked to go to the main office between classes to give their answer to the question. Is there bias in this study?

• Yes

• No

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The question about the theme for prom is posed during the morning announcements.  Students are asked to go to the main office between classes to give their answer to the question.  This is what type of sampling design? 

• Cluster
• Convenience
• Voluntary Response
• SRS

A "fake" treatment that can be given to eliminate the possibility of psychological effects is called ______.

• Anecdotal Evidence

• Control

• Placebo

• Treatment Group

A study of human development showed two types of movies to groups of children. Crackers were available in a bowl, and the investigators compared the number of crackers eaten by children watching the different kinds of movies. One kind of movie was shown at 8 AM (right after the children had breakfast) and another at 11 AM (right before the children had lunch). It was found that during the movie shown at 11 AM, more crackers were eaten than during the movie shown at 8 AM. The investigators concluded that the different types of movies had an effect on appetite.
The results cannot be trusted because

• the study was not double-blind. Neither the investigators nor the children should have been aware of which movie was being shown.
• the investigators were biased. They knew beforehand what they hoped the study would show.
• the investigators should have used several bowls, with crackers randomly placed in each.
• the time the movie was shown is a confounding variable.

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Consider an experiment to investigate the effectiveness of different insecticides in controlling pests and their effects on subsequent yield. What is the best reason for randomly assigning treatment levels (spraying or not spraying) to the experimental units (farms)?

• Randomization makes the experiment easier to conduct since we can apply the insecticide in any pattern rather than in a systematic fashion.
• Randomization will tend to average out all other uncontrolled factors such as soil fertility so that they are not confounded with the treatment effects.
• Randomization makes the analysis easier since the data can be collected and entered into the computer in any order.
• Randomization is required by statistical consultants before they will help you analyze the experiment.

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Which is important in designing a good experiment?
1. Randomization in assigning subjects to treatments
2. Control of potentially confounding variablese
3. Replication of the experiment on a sufficient number of subjects

• 1 and 2
• 1 and 3
• 2 and 3
• All 3

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True or False: Double-blind experiments are only necessary when the experimenters cannot be trusted to act ethically.

• True

• False