psy418 stats exam 2

Using an independent-measures t, the 90% confidence interval for the difference between two population means ranges from 19 to 23. Based on this confidence interval, you can conclude that the difference between the two sample means is _____. 4 points 19 points 21 points 23 points

21

A researcher reports t(22) = 5.30, p < .01 for an independent-measures experiment. How many individuals participated in the entire experiment?

24

. Using an independent-measures t, the 90% confidence interval for the difference between two population means ranges from 19 to 23. Based on this confidence interval, you can conclude that the difference between the two sample means is _____. a. 4 points b. 19 points c. 21 points d. 23 points

A

Decreasing the sample size, while holding the confidence level the same, will do what to the width of your confidence interval? a. make it bigger b. make it smaller c. it will stay the same d. cannot be determined from the given information

A

On average, what value is expected for the t statistic when the null hypothesis is true? a. 0 b. 1 c. 1.96 d. t > 1.96

A

Under what circumstances can a very small treatment effect be statistically significant? a. if the sample size is big and the sample variance is small b. if the sample size and the sample variance are both big c. if the sample size is small and the sample variance is big d. if the sample size and the sample variance are both small

A

Which set of characteristics will produce the smallest value for the estimated standard error? a. a large sample size and a small sample variance b. a large sample size and a large sample variance c. a small sample size and a small sample variance d. a small sample size and a large sample variance

A

What effect does decreasing standard error (in both distributions) have on power, Type I error, and Type II error?

Answer: increases power, doesn't affect Type I error, decreases Type II error

99.9% CI doesn't include 0, alpha level = .01 a. Fail to reject b. Reject c. Non-diagnostic

B

Which of the following accurately describes the chi-square distribution? a. symmetrical with a mean of zero b. positively skewed with all values greater than or equal to zero c. negatively skewed with all values greater than or equal to zero d. symmetrical with a mean equal to n - 1

B

15. In a 95% confidence interval, what is the likelihood that the point estimate accurately estimates the parameter of interest? a. Extremely high b. 5% c. Extremely low d. 95%

C

99% CI includes 0, alpha level = .20 a. Fail to reject b. Reject c. Non-diagnostic

C

A hypothesis test produces a t statistic of t = 2.20. If the researcher is using a two-tailed test with α= .05, how large does the sample have to be in order to reject the null hypothesis? a. at least n = 11 b. at least n = 12 c. at least n = 13 d. at least n = 14

C

What happens to the critical value for a chi-square test if the size of the sample is increased? a. The critical value also increases. b. The critical value decreases. c. The critical value depends on the number of categories, not the sample size. d. The critical value is determined entirely by the alpha level.

C

Which of the following will increase the power of a statistical test? a. Change α from .05 to .01. b. Change from a one-tailed test to a two-tailed test. c. Change the sample size from n = 25 to n = 100. d. None of the other options will increase power.

C

By selecting a larger alpha level, a researcher is ______. a. attempting to make it easier to reject Ho b. better able to detect a treatment effect c. increasing the risk of a Type I error d. All of the above

D

If a researcher is using a t statistic to test a null hypothesis about a population, what information is needed from the population to calculate the t statistic? a. You must know the population mean. b. You must know the population variance or standard deviation. c. You must know the population mean and the variance or standard deviation. d. The t statistic does not require any information about the population

D

If two samples are selected from the same population, under what circumstances will the two samples have exactly the same t statistic? a. If the samples are the same size and have the same variance. b. If the samples are the same size and have the same mean. c. If the samples have the same mean and the same variance. d. If the samples are the same size and have the same mean and have the same variance.

D

If α is held constant at .05, what is the relationship between sample size, the critical region, and the risk of a Type I error? a. As sample size increases, the critical region expands and the risk of a Type I error increases. b. As sample size increases, the critical region shrinks and the risk of a Type I error increases. c. As sample size increases, the critical region expands and the risk of a Type I error decreases. d. There is no relationship between sample size, the critical region, and the risk of a Type I error.

D

What is the likelihood that a 95% CI contains 95% of the scores (e.g., sample means, etc.) in the sampling distribution? a. .9025, or .95 2 b. Unknown c. Zero d. Very low

D

T or F In a repeated measures study, the null hypothesis says that the mean for the sample of difference scores should be equal to zero.

F

T or F: A 95% confidence interval for the mean number of televisions per American household is (1.15, 4.20). For questions 20-22, choose true or false. 95% of all samples should have x-bars between 1.15 and 4.20.

F

T or F: If two samples each have the same mean, the same number of scores, and are selected from the same population, then they will also have identical t statistics.

F

T or F: For an independent-measures study, the width of a confidence interval estimating μ 1- μ2 depends of the size of the difference between M1and M2 .

F, d bar

T or F: The confidence interval states that there's a 95% chance the population mean is equal to the sample mean

FALSE, it is about zero

T or F: the confidence interval states that 95% of ALL SCORES fall into the confidence interval

FALSEEEEEEEEEEEEEEE

T or F: A 95% confidence interval for the mean number of televisions per American household is (1.15, 4.20). For questions 20-22, choose true or false. We are 95% confident that the true mean number of televisions per American household is between 1.15 and 4.20.

T

T or F: Two samples from same population probably will have different t statistics even if they are the same size and have the same mean.

T

Under what circumstances can a very small treatment effect can still be significant? a. if the sample size (n) is very large b. if the sample standard deviation (σ) is very large c. if the standard error of M is very large d. All of the other factors are likely to produce a significant result.

a

Decreasing the confidence level, while holding the sample size the same, will do what to the width of your confidence interval? a. make it bigger b. make it smaller c. it will stay the same d. cannot be determined from the given information

b

If a treatment has a very small effect, then what is a likely outcome for a hypothesis test evaluating the treatment? a. a Type I error b. a Type II error c. correctly reject the null hypothesis d. correctly fail to reject the null hypothesis

b

Which of the following is an accurate definition of a Type I error? a. rejecting a false null hypothesis b. rejecting a true null hypothesis c. failing to reject a false null hypothesis d. failing to reject a true null hypothesis

b

For which of the following situations would a repeated-measures design have the maximum advantage over an independent-measures design?

b. when very few subjects are available and individual differences are small

A researcher administers a treatment to a sample of participants selected from a population with μ = 80. If a hypothesis test is used to evaluate the effect of the treatment, which combination of factors is most likely to result in rejecting the null hypothesis? a. a sample mean near 80 for a small sample b. a sample mean near 80 for a large sample c. a sample mean much different than 80 for a small sample d. a sample mean much different than 80 for a large sample

d

If you increase the sample size and confidence level at the same time, what will happen to the length of your confidence interval? a. make it bigger b. make it smaller a. it will stay the same b. cannot be determined from the given information

d

what is the effect of increasing the sample size on standard error and type I error

decrease standard error no effect on the risk of a type I error

A sampling distribution centered at the null hypothesis has a mean of 0. . If the interval includes 0......

fail to reject null

Confidence intervals with the independent-measures t statistic are used to estimate ________

how much difference there is between population means

d

individual difference between two values in a matched pair (repeated measures t test)

What effect does moving the dotted line to the left (decrease alpha level) have on power, Type I error, and Type II error?

power decreases, type I error decreases, tII error increases

What effect does moving the actual distribution further away from the null distribution have on power, Type I error, and Type II error?

power increase TI no effect TII decrease

A sampling distribution centered at the null hypothesis has a mean of 0. If the interval does not include 0.....

reject null

If the sample size is held constant, which of the following will produce the widest 90% confidence interval for the population mean difference for a repeated-measures study?

smaller Md and larger variability

The null hypothesis for a repeated-measures test states:

the entire population will have a mean difference of 0

What value is estimated with a confidence interval using the repeated-measures t statistic?

the mean for a population of difference scores

Which of the following possibilities is a serious concern with a repeated-measures study?

the results will be influenced by order effects

a CI states that...

there's 95% confidence that U (pop mean) is within the confidence interval

In an independent-measures hypothesis test, what must be true if t = 0?

two sample means must be equal