4.2-4.3 Stats Quiz Review

In an experiment, an observed effect so large that it would rarely occur by chance is called....

• an outlier

• influential

• statistically significant

• bias

• replication

A stratified random sample addresses the same issues as which of the following experimental designs?

• A block design

• A double-blind experiment

• An experiment with a placebo

• A completely randomized design

• A confounded, nonrandomized study

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Which of the following is not a major principle of good design for all experiments?

• Comparison

• Replication

• Blocking

• Randomization

• All of these are important principles for every experiment

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The essential difference between an experiment and an observational study is that

• observational studies may have confounded variables, but experiments never do.

• in an experiment, people must give their informed consent before being allowed to participate.

• observational studies are always biased.

• observational studies cannot have response variables.

• an experiment imposes treatments on the subjects, but an observational study does not.

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In order to assess the effects of exercise on reducing cholesterol, a researcher took a random sample of fifty people from a local gym who exercised regularly and another random sample of fifty people from the surrounding community who did not exercise regularly. They all reported to a clinic to have their cholesterol measured. The subjects were unaware of the purpose of the study, and the technician measuring the cholesterol was not aware of whether or not subjects exercised regularly.

This is a(n)...

• observational study

• experiment, but not a double blind experiment

• double blind experiment

• matched pairs experiment

• block design

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In order to assess the effects of exercise on reducing cholesterol, a researcher took a random sample of fifty people from a local gym who exercised regularly and another random sample of fifty people from the surrounding community who did not exercise regularly. They all reported to a clinic to have their cholesterol measured. The subjects were unaware of the purpose of the study, and the technician measuring the cholesterol was not aware of whether or not subjects exercised regularly.

Which of the following best describes the inferences the researcher can make based on his results?

• He can make inferences about cause and effect, but not about the populations from which the samples were taken.

• He can make inferences about the populations from which the samples were taken, but not about cause and effect.

• He can make inferences about both cause and effect and the populations from which the samples were taken.

• He cannot make inferences about either cause and effect or the populations from which the samples were taken.

• There is not enough information to make judgments about the scope of inference.

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A market research company wishes to find out whether the population of students at a university prefers brand A or brand B of instant coffee. A random sample of students is selected, and each one is asked to try brand A first and then brand B (or vice versa, with the order determined at random). They then indicate which brand they prefer. The response variable is

• whether brand A or B is tried first

• which brand they prefer

• coffee

• the identity of the student

• none of these

The most important advantage of experiments over observational studies is that

• experiments are usually easier to carry out.

• experiments can give better evidence of causation.

• confounding cannot happen in experiments.

• an observational study cannot have a response variable.

• observational studies cannot use random samples.

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Does caffeine improve exam performance? Suppose all students in the 8:30 section of a course are given a "treatment" (two cups of coffee) and all students in the 9:30 section are not permitted to have any caffeine before a mid-term exam.

Unfortunately, any systematic difference between the two sections on the exam might be due to the fact that the 8:30 and 9:30 classes have different instructors. This is an example of

• placebo effect

• bias

• confounding

• observational study

• stratification

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Does caffeine improve exam performance? Suppose all students in the 8:30 section of a course are given a "treatment" (two cups of coffee) and all students in the 9:30 section are not permitted to have any caffeine before a mid-term exam.

The response variable in this study is..

• two cups of coffee

• the time the class is held

• class attendance

• teacher's performance

• exam performance

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