Question

Researcher John is interested in the extent to which stress influences human memory. He has run a study in which a random sample of 25 participants has been told that they will be required to give a lecture in front of a large audience. Giving a speech in front of a large audience is considered a stressful event by many people.

While the participants were busy preparing for their presentation, they were asked to complete a memory task. It is known that in “typical” situations (without a lot of stress), the mean number of questions on the memory task is 53. The observed mean number of correctly-answered questions for these 25 participants is X ̄ = 48. Assume that the standard deviation of memory scores in the population is 7.

The null hypothesis is that the manipulation did not affect the scores. The alternative hypothesis is that the true mean number of correctly answered questions is smaller than 53; that is, the stress of the preparation for the presentation hurts performance. The hypotheses may be written formally:

H0 : μ=53 HA : μ<53

(a) Carry out the test and give the p value.

(b) Explain in words what the p value means. The p value is the probability that...

(c) How strong is the evidence that, for this memory test, the mean number of correctly answered questions in stressful situations is smaller that the mean number of correctly answered questions in a “typical” situation?

Answer 1