Stats PY 211 Exam 3

The t distribution is similar to the z distribution except -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 -All of the above

all the above

A researcher conducts a study measuring comparing the obesity rate in a small community to the known obesity rate in the United States. 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

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

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 asks a sample of brothers and sisters to rate how positive their family environment was during childhood. In this study, the differences in ratings between each brother and sister pair were compared. The type of design described here is called a

Matched samples design

a researcher has participants rate the likability of a sexually promiscuous person described in a vignettes 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, the result is not significant, t= 0

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

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 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±D) 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.

There was a significant difference: Women found this trait to be important

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 each exam scores is unknown, what type of t test is appropriate for analyzing differences between these classes?

Two-independent sample t test

A researcher reports that mean ratings of linking 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 computes the mean difference in locomotion in a sample of 12 rats before and 30 minutes after an injection of amphetamine. Rats were placed in a box with infrared beams. The number of times rats crossed the beams was used as a measure of locomotion. The mean difference in locomotion was 6.2±8.4 (MD±SD), and this difference was significant. What is the effect size for this result using estimated Cohen's d?

d=0.74 (medium effect)

A researcher reports that the mean difference in the body weight of rats following pharmacological versus control treatments 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 professor compares scores on a competency exam among students at two times during a single semester. What type of t test is most appropriate for this study?

related sample t test

A researcher compares the difference in the amount of texting by students in class during the first week and last week of classes. The type of design described here is called a

repeated measures design

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

±2.086

A researcher matched 30 participants on intelligence (hence 15 pairs of patients), and then compared differences in emotional responsiveness to two experimental stimuli between each pair. For this test, what are the critical values, assuming a two-tailed test at a .05 level of significance?

±2.145