Exam 9: Testing Means: One-Sample and Two-Independent-Sample T Tests

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 for a two-tailed test.

A one-sample t test will be t = 0 when the mean difference is equal to 0.

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.

$\eta$ ² is a more conservative estimate than $\omega$ ².

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 estimates 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 for a two-tailed 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?

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.

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 must know the population variance in order to compute a t test.

The mean crying time of infants during naptime at a local preschool is 12 min.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)min.Test whether this new naptime routine reduced crying time at a .05 level of significance.

Effect size measures are an estimate of the size of an effect in a population.

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?

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

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?

A researcher computes a two-independent-sample t test and finds that the result is undefined (the denominator is equal to 0).This always happens when two groups do not differ (i.e.,the mean difference is equal to 0).

Normality is the assumption that data in the population are normally distributed.

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 researcher reports that the mean time it takes to complete an experimental task is 1.4 ± 8.0 (M ± SD)s.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 t statistic estimates the standard error by using the sample variance to approximate the population variance.

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 $\eta$ ² to interpret the effect size for this result.