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Exam 11: Power

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Question 31

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In an experiment, if the effect of the independent variable and alpha remain the same and N increases, _________.

A) power increases
B) power decreases
C) power remains the same
D) cannot be determined

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Question 32

Multiple Choice

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P _real is defined as _________.

A) the probability of getting a plus with any subject in the sample of the experiment when the independent variable has a real effect
B) the probability of getting a plus with any subject in the sample of the experiment when the independent variable has no effect
C) the probability of getting a plus with any subject in the sample of the experiment when chance alone is at work
D) the probability of getting a plus with any subject in the sample of the experiment when the independent variable has a real effect in the direction predicted by the directional H ₁

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Question 33

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Maximizing the power of an experiment _________.

In an experiment the value for beta has been shown to be .7503. What is the power of this experiment?

The concept of statistical power applies only to the sign test.

A wine company has retained you as a consultant to help evaluate the taste preference for their wine compared to the market leader. You plan to give 20 subjects a taste of both wines and ask them to rate the wines on a 10 point scale. The order of presentation is randomized so there is no order effect. Your plan is to analyze the results using the sign test. If the size of the difference is such that P _real = 0.80, what is the power of your experiment to detect a preference for one wine or the other? Use a = 0.05_{2 tail}.

A real effect of the independent variable is defined as _________.

In an experiment with N = 14 and P _real = 0.10, what is the power using a = .01_{2 tail}?

Using sample data, it is impossible to prove with certainty that H ₀ is true.

b = 1 ?2- a .

Decreasing beta will generally cause a to increase.

In an experiment, if the analysis of the data does not allow us to reject the null hypothesis, this can only be so because we do not have enough experimental power to reject H ₀ . Why?

List three variables (not including beta) that affect power and state how increases in the variables affect power.

In an experiment where the experimental effect is such that P _real = 0.70 and N = 14, what is the power of the experiment? Use a = 0.05_{2 tail} with the sign test.

You are considering testing a new drug that is supposed to facilitate learning in mentally retarded children. Because there is relatively little known about the drug, you plan to use a nondirectional alternative hypothesis. Since your resources are limited, you can test only 20 subjects. The subjects will be run in a repeated measures design and the data will be analyzed with the sign test, using a = 0.05_{2 tail}. What is the power this time?

The greater the sample size the greater the power.

One can increase power by _________.

With other factors held constant, as the effect of the independent variable decreases, power will _________ and the probability of a Type II error will _________.

If beta = 0.7500, what is the power of the experiment?

When is it important to know the power of an experiment? Why?