CH 9 Data Analysis

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?

crying time was significantly receded among infants given the sucrose solution prior to a heel prick

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?

d = 0.05; small effect size

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?

d = 0.33; medium effect size

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?

d = 0.53; medium effect size

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?

d = 0.88; large effect size

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?

eta-squared

A researcher reports a significant mean difference in a given population. If she computes both eta-squared and omega-squared to measure the effect size, then which estimate will be the most conservative?

omega-squared

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?

two-independent sample t test

State the critical value(s) for the following two-tailed t test at a .05 level of significance: t().

±1.645 and ±1.96

Computing a two-independent sample t test is appropriate when

(ALL OF THE ABOVE) different participants are assigned to each group, the population variance is unknown, participants are observed one time

A researcher selects a sample of 32 participants who are assigned to participate in a study with one group. What are the degrees of freedom for this test?

31

Two researchers (A and B) compute a two-independent sample t test. For both tests, the mean difference between the two groups is 10, but the standard error is smaller for Researcher A. Which test is more likely to result in a decision to reject the null hypothesis?

Researcher A

Eta-squared is computed ______ for the one-sample, and the two-independent sample t tests.

Similarly

A researcher conducts two t tests. Test 1 is a two-tailed test with a smaller sample size at a .05 level of significance. Test 2 is a two-tailed test with a larger sample size at a .05 level of significance. What do you know about the degrees of freedom for each test?

Test 2 is associated with larger degrees of freedom.

The average response time to a bank robbery is about 9 minutes. A local community wants to improve on this time, so they implement advanced training seminars. They find that the new response time for a sample of 36 police officers is 8±4.2 (M±SD) minutes. Test whether this advanced training seminar reduced response time at a .05 level of significance.

This advanced training seminar did not reduce response time, t(35) = -1.43, p > .05.

A researcher selects a sample of 16 women and asks them to rate how important a sense of humor is in someone they want a long-term relationship with. She records scores averaging 1.6±0.8 (M±SD) on a rating scale from -3 (not important at all) to +3 (very important). Assuming that an average score of 0 is the null hypothesis, test whether or not women find this trait important at a .05 level of significance.

Women found this trait to be important, and this result was significant, t(15) = 8.00, p < .05.

A researcher reports that stress levels among nurses are higher compared to stress levels in the general population, t(20) = 2.086, p = .05 (d = .12). Was this a one-tailed or a two-tailed test?

a two-tailed test because the p value is equal to .05

The t distribution is similar to the z distribution except

(ALL OF THE ABOVE) it is associated with greater variability, it is characterized by "thicker" tails compared with the z distribution, it is associated with scores being more likely in the tails of the distribution

Computing a one-sample t test is appropriate when

(ALL OF THE ABOVE) participants are assigned to only one group, the population variance is unknown, participants are observed one time

Which of the following is an assumption for computing any type of independent sample t test?

(All of the above)- Data in the population being sampled are normally distributed.; Data were obtained from a sample that was selected using a random sampling procedure.; The probabilities of each measured outcome in a study are independent.

State the critical value(s) for a t test using a .05 level of significance in the lower tail only: t(24).

-1.711

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.

12% of the variability in marketing effectiveness can be accounted for by the new marketing strategy.

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

Because it makes little sense to report the size of an effect that you just concluded doesn't exist.

Which measure of effect size is most commonly reported with a t test?

Cohen's d

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

Equal variances

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.

Exam scores were the same between groups, t(18) = 1.00, p > .05.

Is a one-sample t test reported differently for one-tailed and two-tailed tests?

No, the same values are reported.

Two researchers (A and B) compute a one-sample t test. For both tests, the mean difference between the sample and value stated in the null hypothesis is 5, but the standard error is smaller for Researcher A. Which test is more likely to result in a decision to reject the null hypothesis?

Researcher A

Two researchers (A and B) compute a two-independent sample t test. For both tests, the standard error is the same, but the mean difference between the groups is larger for Researcher A. Which test is more likely to result in a decision to reject the null hypothesis?

Researcher A.

Two researchers (A and B) compute a one-sample t test. For both tests, the standard error is the same, but the mean difference between the sample and value stated in the null hypothesis is smaller for Researcher A. Which test is more likely to result in a decision to reject the null hypothesis?

Researcher B

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.

Risk levels in the population shifted 0.64 standard deviations below the mean.

A researcher conducts two t tests. Test 1 is a one-tailed test with a smaller sample size at a .05 level of significance. Test 2 is a one-tailed test with a larger sample size at a .05 level of significance. What do you know about the critical values for each test?

Test 2 is associated with smaller critical values

The mean crying time of infants during naptime at a local preschool is 12 minutes. The school implements a new naptime routine in a sample of 25 infants and records an average crying time of 8±4.6 (M±SD) minutes. Test whether this new naptime routine reduced crying time at a .05 level of significance.

The new naptime routine significantly reduced crying time, t(24) = -4.35, p < .05.

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?

The population variance must be known.

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.

There is not enough information to answer this question.

A key difference between a t statistic and a z statistic is that the standard error is ________ to compute a t statistic.

estimated

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

n2 = 0.43 (large effect size)

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?

no, this result is not significant

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?

no, this result is not significant t(30)=0

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?

one-sample t test

A researcher records the number of distracters (such as noises) that preschool-aged children ignore while watching a popular Sunday morning cartoon show. Assuming that the population variance is unknown, what type of t test is appropriate for this study?

one-sample t test

You read about a study testing whether night shift workers sleep the recommended 8 hours per day. Assuming that the population variance of sleep (per day) is unknown, what type of t test is appropriate for this study?

one-sample t test

The estimated standard error in the t statistic uses the ________ to estimate the ________ when the population variance is unknown.

sample variance; population variance

The ________ is an inferential statistic used to determine the number of standard deviations in a t distribution that a sample mean deviates from the mean value or mean difference stated in the null hypothesis.

t statistic

Which of the following summarizes a t test that was significant and associated with a large effect size?

t(12) = 2.95, p < .05, d = .82

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?

the pooled population variance

As a requirement for the t test, researchers compute any type of t test with samples selected from populations in which

the population variance is unknown

A professor compares final exam scores in his psychology class to final exam grades in another comparable professor's class. Assuming that the population variance of exam scores is unknown, what type of t test is appropriate for analyzing differences between these classes?

two-independent sample t test

A researcher conducts a study measuring differences in brain activity among rats placed on either a continuous or intermittent reward schedule. Assuming that the population variance in unknown, what type of t test is appropriate for this study?

two-independent sample t test

State the critical value(s) for a t test using a two-tailed test at a .05 level of significance: t(20).

±2.086