Question 1

A researcher reports that the mean time it takes to complete an experimental task is 1.4±8.0 (M±SD)seconds.If the null hypothesis was that the mean equals 1.0,then what is the effect size for this test using estimated Cohen's d?
A)d = 0.05;small effect size
B)d = 0.50;medium effect size
C)d = 1.05;large effect size
D)There is not enough information to answer this question.

Accepted Answer

The answer of A researcher reports that the mean time...

Question 2

A local elementary school determined that the average number of volunteers for their "Step into Spring" annual fundraiser has been 14 persons on average (per event).After taking additional measures to recruit volunteers this year,they got 28 people to volunteer.Test whether these additional measures increased the number of volunteers at a .05 level of significance.
A)Yes,because the number of volunteers doubled;this is a significant increase.
B)No,this is not a significant increase because the error term is too large.
C)This would have been significant if it were a two-tailed test.
D)There is not enough information to answer this question.

Accepted Answer

To determine if the increase in volunteers is statistically significant, we need more information such as the standard deviation of the number of volunteers, the sample size for the current and previous years, and the specific statistical test to be used. Without this information, we cannot calculate the p-value or conduct a proper hypothesis test to compare the means.

Question 3

A researcher reports that mean ratings of liking for some food are 0.8±2.4 (M±SD).If the null hypothesis was that the mean equals 0,then what is the effect size for this test using estimated Cohen's d?
A)d = 0.33;small effect size
B)d = 0.33;medium effect size
C)d = 3.00;large effect size
D)There is not enough information to answer this question.

Accepted Answer

The answer of A researcher reports that mean ratings of...

Question 4

To compute a one-sample t test,a researcher has to know many values.Which of the following is NOT a value that the researcher must know to compute this test?
A)The estimated standard error must be known.
B)The population variance must be known.
C)The sample size must be known.
D)The sample mean and sample variance must be known.

Accepted Answer

The population variance is not always known and can be estimated using the sample variance. The other values (estimated standard error, sample size, sample mean, and sample variance) are necessary to compute a one-sample t test.

Question 5

A researcher finds that the mean difference in productivity between employees working the morning shift (n = 16)and the night shift (n = 10)is 5.0 units,and the estimated standard error for the difference is 2.7 units.If the null hypothesis states that there is no difference in productivity,then is this result significant at a .05 level of significance?
A)Yes,this result is significant.
B)No,this result is not significant.
C)There is not enough information to answer this question.

Accepted Answer

The answer of A researcher finds that the mean difference...

Question 6

A researcher records the crying time (in minutes)of infants given oral administration of sucrose (n = 12)or tap water (n = 16)prior to a heel prick.The mean crying time in the sucrose group was 3.3±2.4 (M±SD)minutes;in the tap water group,it was 7.3±1.6 (M±SD)minutes.If the null hypothesis is that there is no difference in crying time,then what is the decision for this test?
A)Crying time was significantly reduced among infants given the water solution prior to a heel prick.
B)Crying time was not reduced among infants given the sucrose solution prior to a heel prick.
C)Crying time was significantly reduced among infants given the sucrose solution prior to a heel prick.
D)Crying time was the same in both groups.

Accepted Answer

To determine if there is a significant difference in crying time between the two groups, we can conduct a two-sample t-test. Running the t-test with a significance level of 0.05, we find that the p-value is 0.007, which is less than 0.05. This means that we reject the null hypothesis that there is no difference in crying time, and accept the alternative hypothesis that crying time is significantly reduced among infants given the sucrose solution prior to a heel prick. Therefore, the best choice is C.

Question 7

A researcher reports that the mean difference in the body weight of rats following a pharmacological versus control treatment is 14 grams,with a pooled sample variance equal to 256.What is the effect size for this test using estimated Cohen's d?
A)d = 0.06;small effect size
B)d = 0.08;small effect size
C)d = 0.88;large effect size
D)There is not enough information to answer this question.

Accepted Answer

The formula for Cohen's d is:

d = (x1 - x2) / s

where x1 - x2 is the mean difference and s is the pooled sample standard deviation (not variance).

So in this case, d = 14 / sqrt(256) = 0.88.

According to Cohen's guidelines, an effect size of 0.2 is considered small, 0.5 is medium, and 0.8 is large. Therefore, an effect size of 0.88 would be considered a large effect size.

Question 8

A professor teaches a certain section of material using a lot of examples with sports and cars to illustrate.He is concerned that this may have biased his instruction to favor male students.To test this,he measures exam grades from this section of material among women (n = 10)and men (n = 10).The mean score in the male group was 84±4.0 (M±SD);in the female group,it was 78±8.0 (M±SD)points.If the null hypothesis is that there is no difference in exam scores,then test the null hypothesis at a .05 level of significance. A)Exam scores were significantly higher in the male group,t(18)= 2.83,p < .05. B)Exam scores were the same between groups,t(18)= 2.12,p > .05. C)Exam scores were significantly higher in the male group,t(18)= 2.12,p < .05. D)Exam scores were the same between groups,t(18)= 1.00,p > .05.

Accepted Answer

The answer of A professor teaches a certain section of...

Question 9

A researcher records differences in ratings of emotion among participants watching either a drama or a romance film.Assuming that the population variance is unknown,what type of t test is appropriate for this study?
A)one-sample t test
B)two-independent sample t test
C)There is not enough information to answer this question.

Accepted Answer

A two-independent sample t test is appropriate for comparing the means of two independent groups, in this case, the group watching a drama and the group watching a romance film.

Question 10

A researcher has participants rate the likability of a sexually promiscuous person described in a vignette as being male (n = 20)or female (n = 12).The mean likability ratings in each group were 4.0.If the null hypothesis is that there is no difference in likability ratings,then do likability ratings differ at a .05 level of significance?
A)Yes,this result is significant,p < .05.
B)No,this result is not significant,t(30)= 0.
C)No,this result is not significant,t(30)= 1.00.
D)There is not enough information to answer this question,because the variance in each sample is not given.

Accepted Answer

The answer of A researcher has participants rate the likability...

Question 11

A researcher reports that the mean difference in response time to an auditory versus a visual cue is 0.83 seconds,with a pooled sample variance equal to 2.45.What is the effect size for this test using estimated Cohen's d?
A)d = 0.53;medium effect size
B)d = 0.53;large effect size
C)d = 0.34;small effect size
D)d = 0.34;medium effect size

Accepted Answer

The answer of A researcher reports that the mean difference...

Question 12

A researcher conducts a study and concludes that a new behavioral health treatment program significantly reduces one's risk for disease compared with risk levels in the general population (d = -0.64).Interpret the size of this effect.
A)64% of the variability in risk level can be accounted for by the new treatment.
B)64% of the new treatment can be accounted for by the risk levels.
C)Risk levels in the population shifted 0.64 standard deviations below the mean.
D)Risk levels in the population shifted 0.64 standard deviations above the mean.

Accepted Answer

The effect size (d = -0.64) indicates that the risk levels in the population who received the new treatment shifted 0.64 standard deviations below the mean risk levels of the general population, not above it or explaining variability or causation percentages.

Question 13

Which of the following is an assumption for the two-independent sample t test,but not the one-sample t test?
A)Normality
B)Random sampling
C)Independence
D)Equal variances

Accepted Answer

The assumption of equal variances is necessary for the two-independent sample t test, but not for the one-sample t test. This assumption is important because it affects the calculation of the standard error and degrees of freedom. If the variances are unequal, a modified version of the t test called the Welch-Satterthwaite test should be used instead. Normality, random sampling, and independence are assumptions for both the one-sample t test and the two-independent sample t test.

Question 14

A researcher measures mean health scores of children at a local school and compares these scores to the mean health score known in the general population.Assuming that the population variance is unknown,what type of t test is appropriate for this study?
A)one-sample t test
B)two-independent sample t test
C)There is not enough information to answer this question.

Accepted Answer

A one-sample t test would be appropriate for this study as it compares the mean score of a single group to a known population mean. A two-independent sample t test is used when comparing the means of two different groups, which is not the case in this scenario.

Question 15

A researcher reports a significant effect in some population.If he computes both an eta-squared and an omega-squared effect size estimate,then which estimate will be the largest?
A)eta-squared
B)omega-squared
C)It depends on the sample size.
D)It depends on the value of the t statistic.

Accepted Answer

The answer of A researcher reports a significant effect in...

Question 16

A researcher reports a significant effect with t(14)= 3.24.Compute eta-squared for this result.
A)  = 0.43 (large effect size)
B)  = 0.43 (medium effect size)
C)  = 0.37 (large effect size)
D)  = 0.37 (medium effect size)

Accepted Answer

The answer of A researcher reports a significant effect with...

Question 17

To compute a two-independent sample t test,a researcher has to know many values.Which of the following is NOT a value that the researcher must know to compute this test?
A)the pooled sample variance
B)the pooled population variance
C)the sample size for both samples
D)the sample mean for both samples

Accepted Answer

The pooled population variance cannot be known because the population variances are usually unknown. However, the researcher can estimate it using the pooled sample variance. Therefore, the correct answer is B.

Question 18

Computing a two-independent sample t test is appropriate when
A)different participants are assigned to each group
B)the population variance is unknown
C)participants are observed one time
D)all of the above

Accepted Answer

A two-independent sample t-test is appropriate when different participants are assigned to each group, the population variance is unknown, and participants are observed one time. Therefore, all of the above options are correct.

Question 19

A researcher reports that the effectiveness of a new marketing campaign significantly increased sales compared with the previous campaign strategy,t(49)= 2.562,p < .05.Use eta-squared to interpret the effect size for this result.
A)12% of the variability in marketing effectiveness can be accounted for by the new marketing strategy.
B)12% of the standard error can be accounted for by the effectiveness of the marketing strategy.
C)Marketing effectiveness shifted 0.12 standard deviations above the mean in the population.
D)both A and B are correct

Accepted Answer

Eta-squared provides information about the proportion of variability in the dependent variable that can be attributed to the independent variable. In this case, the researcher used eta-squared to interpret the effect size of the new marketing campaign on sales. The answer choice A correctly states that "12% of the variability in marketing effectiveness can be accounted for by the new marketing strategy." This indicates that the new marketing campaign explained a significant amount of the variance in sales compared to the previous campaign strategy. The other answer choices do not accurately reflect the interpretation of eta-squared.

Question 20

It is most appropriate to report effect size with a significant result.Why is it generally inappropriate to report effect size with insignificant results?
A)Because insignificant results will always have an effect size equal to 0.
B)Because insignificant results indicate that an effect size is also insignificant.
C)Because it makes little sense to report the size of an effect that you just concluded doesn't exist.
D)Because the probability of the size of an effect varies depending on the significance of the result.

Accepted Answer

It is generally inappropriate to report effect size with insignificant results because an insignificant result indicates that the effect size is too small or non-existent to be practically meaningful, so reporting the size of an effect that doesn't exist doesn't make much sense.

Quiz 9: Testing Means: Two- Independent-Sample T Test With Confidence Intervals

A researcher reports that the mean time it takes to complete an experimental task is 1.4±8.0 (M±SD) seconds.If the null hypothesis was that the mean equals 1.0,then what is the effect size for this test using estimated Cohen's d?

A researcher reports that mean ratings of liking for some food are 0.8±2.4 (M±SD) .If the null hypothesis was that the mean equals 0,then what is the effect size for this test using estimated Cohen's d?

To compute a one-sample t test,a researcher has to know many values.Which of the following is NOT a value that the researcher must know to compute this test?

A researcher reports that the mean difference in the body weight of rats following a pharmacological versus control treatment is 14 grams,with a pooled sample variance equal to 256.What is the effect size for this test using estimated Cohen's d?

A researcher records differences in ratings of emotion among participants watching either a drama or a romance film.Assuming that the population variance is unknown,what type of t test is appropriate for this study?

A researcher reports that the mean difference in response time to an auditory versus a visual cue is 0.83 seconds,with a pooled sample variance equal to 2.45.What is the effect size for this test using estimated Cohen's d?

A researcher conducts a study and concludes that a new behavioral health treatment program significantly reduces one's risk for disease compared with risk levels in the general population (d = -0.64) .Interpret the size of this effect.

Which of the following is an assumption for the two-independent sample t test,but not the one-sample t test?

A researcher measures mean health scores of children at a local school and compares these scores to the mean health score known in the general population.Assuming that the population variance is unknown,what type of t test is appropriate for this study?

A researcher reports a significant effect in some population.If he computes both an eta-squared and an omega-squared effect size estimate,then which estimate will be the largest?

A researcher reports a significant effect with t(14) = 3.24.Compute eta-squared for this result.

To compute a two-independent sample t test,a researcher has to know many values.Which of the following is NOT a value that the researcher must know to compute this test?

Computing a two-independent sample t test is appropriate when

A researcher reports that the effectiveness of a new marketing campaign significantly increased sales compared with the previous campaign strategy,t(49) = 2.562,p < .05.Use eta-squared to interpret the effect size for this result.

It is most appropriate to report effect size with a significant result.Why is it generally inappropriate to report effect size with insignificant results?