Question

WEEK 7, PRACTICE QUESTIONS (FROM THE BOOK)

Prerequisites

•   All material presented in the Logic of Hypothesis Testing chapter

1. An experiment is conducted to test the claim that James Bond can taste the difference between a Martini that is shaken and one that is stirred. What is the null hypothesis?

2. The following explanation is incorrect. What three words should be added to make it correct?

The probability value is the probability of obtaining a statistic as different (add three words here) from the parameter specified in the null hypothesis as the statistic obtained in the experiment. The probability value is computed assuming that the null hypothesis is true.

3. Why do experimenters test hypotheses they think are false?

4. State the null hypothesis for:

a. An experiment testing whether echinacea decreases the length of colds.

b. A correlational study on the relationship between brain size and intelligence.

c. An investigation of whether a self-proclaimed psychic can predict the outcome of a coin flip.

d. A study comparing a drug with a placebo on the amount of pain relief. (A one-tailed test was used.)

5. Assume the null hypothesis is that μ = 50 and that the graph shown below is the sampling distribution of the mean (M). Would a sample value of M= 60 be significant in a two-tailed test at the .05 level? Roughly what value of M would be needed to be significant?

6. A researcher develops a new theory that predicts that vegetarians will have more of a particular vitamin in their blood than non-vegetarians. An experiment is conducted and vegetarians do have more of the vitamin, but the difference is not significant. The probability value is 0.13. Should the experimenter’s confidence in the theory increase, decrease, or stay the same?

7. A researcher hypothesizes that the lowering in cholesterol associated with weight loss is really due to exercise. To test this, the researcher carefully controls for exercise while comparing the cholesterol levels of a group of subjects who lose weight by dieting with a control group that does not diet. The difference between groups in cholesterol is not significant. Can the researcher claim that weight loss has no effect?

8. A significance test is performed and p = .20. Why can’t the experimenter claim that the probability that the null hypothesis is true is .20?

9. For a drug to be approved by the FDA, the drug must be shown to be safe and effective. If the drug is significantly more effective than a placebo, then the drug is deemed effective. What do you know about the effectiveness of a drug once it has been approved by the FDA (assuming that there has not been a Type I error)?

10. When is it valid to use a one-tailed test? What is the advantage of a one-tailed test? Give an example of a null hypothesis that would be tested by a one-tailed test.

11. Distinguish between probability value and significance level.

Answer 1

1

Null hypothesis: H₀ = James bond cannot taste the difference between a Martini that is shaken and one that is stirred.

Null hypothesis is the statement of no effect, so we have molded our statement accordingly.

2.

The probability value is the probability of obtaining a statistic as different from or more from the parameter specified in the null hypothesis as the statistic obtained in the experiment. The probability value is computed assuming that the null hypothesis is true.

3.

There are many reasons for testing hypothesis that they think are false:

• To establish directionality of the experiment.
• To place the burden of the proof on the alternative hypothesis.
• To ensure that the experimental data supports their judgements about the relevant hypothesis under consideration.

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