# Stat 200 7361 – quiz 3: 100%

Quiz 3

(8 points for each problem; total of 80 points maximum). You must show how a numerical answer is obtained to get full credit.

1. Imagine a sample of 15 subjects with a mean score of 10 and standard error of 3. What’s the upper limit for the 95% confidence interval of the mean?

(Hint: use t-distribution)

2. A researcher believed that there was a difference in the amount of time boys and girls at 7th grade studied by using a two-tailed t test. Which of the following is the null hypothesis?

a. Mean of hours that boys studied per day was equal to mean of hours that girls studied per day

b. Mean of hours that boys studied per day was smaller than or equal to mean of hours that girls studied per day

c. Mean of hours that boys studied per day was greater than mean of hours that girls studied per day

d. Mean of hours that boys studied per day was smaller than mean of hours that girls studied per day

3. A teacher hypothesized that in her class, grades of girls on a chemistry test were the same as grades of boys. If the probability value of her null hypothesis was 0.56, it suggested:

c. We failed to reject the null hypothesis

d. The null hypothesis was rejected

4. A researcher randomly selected 16 boys and 16 girls in a high school and then he measured their weights. The data are listed below:

Frequency

n

Mean (kg)

Variance*

Boys

16

45.5

2.30

Girls

16

40.3

2.30

*Variance =

What is the margin of error of the difference in means (use t-distribution)?

5. A research wants to examine whether a series of interventions affects children’s weight. He has four experimental groups: Group A provides children safe water, group B provides children supplementary food, group C provides children Vitamin A supplements, and group D provides nutrition education to the children’s mothers. If he wants to compare the mean of children’s weights of each group, he need to keep in mind that as he make several comparison, he have a (an) ____ chance of a Type I error

a. Decreased

b. Increased

c. Identical

d. Double

6. A professor wants to test all possible pairwise comparisons among five means. If we need to maintain an experiment –wise alpha of 0.05, what is the error rate per comparison after applying Bonferroni correction?

7. True or False. If a null hyothesis is not rejected by a 2-tailed test, then the null hypothesis cannot be rejected under a 1-tailed test.

8. _____A researcher conducted a study to investigate effect of weight loss for patients takkng diet A and diet B. : = vs. : < . The null hypothesis was highly significant (rejected) at α<0.001. Select all the correct answers.

(a) The difference for these two diets must be very large.

(b) The difference for these two diets may or many not be large.

(c) One diet is 1000 times nore effective than the other.

(d) One diet is more effective than the other but the magnitude of the effect is not known.

9. Which of the following can increase power?

a. Decreasing standard deviation

b. Increasing standard deviation

c. Increasing both means but keeping the difference between the means constant

d. Increasing both means but making the difference between the means smaller

10. ___ Which of following descriptions are correct under any study condition? Select all that apply.

a. Increasing the power will increase the probability of type I error

b. Increasing the significance level (i.e. from 0.05 level to 0.01 level) will increase power

c. Decreasing the significance level (i.e. from 0.01 level to 0.05 level) will increase power

d. Increasing power will decrease the probability of type I error

e. Increasing power has no effect on type I error

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