PSY 305 Assignment 1 - REVISED 1. A researcher gives a group of 25 participants a memory word-memory task. For this task, the average number of words...

PSY 305 Assignment 1 - REVISED

1. A researcher gives a group of 25 participants a memory word-memory task. For this

task, the average number of words remembered in the population is 24 with a

standard deviation of 6. She teaches them a memory technique to use which she

expects will improve their ability to remember. She finds that her sample remembers

average 30 words.

a. What is the research hypothesis?

b. Is this a one or two tailed hypothesis?

c. What is the null hypothesis?

d. What is the z value?

e. What is the critical value for α = .05?

f. What do you conclude?

g. EXTRA CREDIT: What is the exact probability for this outcome (in other

words, the percentage of the normal curve greater than the z score)? Is this

probability greater or smaller than the alpha (α) level of .05?

2. A professor has been teaching statistics for many years. His records show that

historically the overall mean for final exam scores is 85 with a standard deviation of

12 This year he used a different teaching method, and he wants to test whether this

year’s class (the sample) is statistically different from the past classes (the population).

The mean score for the 36 students in this year’s class is 80.

a. What is the research hypothesis?

b. Is this a one or two tailed hypothesis?

c. What is the null hypothesis?

d. Calculate the z value.

e. What is the critical value for α = .05?

f. What do you conclude?

g. EXTRA CREDIT: What is the exact probability for this outcome (in other

words, the percentage of the normal curve greater than the absolute value of

the z score)? Is this probability greater or smaller than the alpha (α) level of

.05?

3. A medical resercher is studying the effect of Vitamin Z on people’s cholesterol level.

In reality, Vitamin Z does not affect cholesterol, but the researcher concludes that the

vitamin does lower cholesterol.

Has the researcher made a Type I error or a Type II error? Explain your answer.