Psych 311 exam 3
A measure of the size of an effect in a population is called
effect size
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
What are the two decisions that researchers can make in hypothesis testing?
retain or reject the null hypothesis
State the critical value(s) for a t test using a two-tailed test at a .05 level of significance: t(20).
±2.086
When reporting the results of a one-sample z test using APA format, the ________ does not need to be reported.
critical values
Is a one-sample z test reported differently for one-tailed and two-tailed tests?
No, the same values are reported.
A researcher conducts two studies. Each study was a one-sample z test. Both studies placed the rejection region in both tails and measured the same sample mean. The alpha level in Study 1 was larger than the alpha level used in Study 2. Which study is associated with greater power to detect an effect?
Study 1
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 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
The criteria for a decision regarding the value stated in a null hypothesis is set by the
level of significance
The power of the decision-making process is
stated by an alpha level
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
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
Which of the following is an assumption for computing any type of independent sample t test?
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.
Which of the following is an assumption for the two-independent sample t test, but not the one-sample t test?
Equal variances
A researcher reports that the size of an effect in some population is d = 0.88. Which of the following is an appropriate interpretation for d?
Mean scores shifted 0.88 standard deviations in the population.
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
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 B.
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.
Which of the following statements regarding the null hypothesis is true?
The null hypothesis always makes statements about a population parameter.
A researcher computes a test statistic and finds that the p value for this test is .03. What does this result mean?
There is a 3% likelihood of obtaining the test statistic value, if the null were true.
________ allows researchers to describe (1) how far mean scores have shifted in the population, or (2) the percentage of variance that can be explained by a given variable.
effect size
The one-sample z test is a hypothesis test used to test hypotheses
concerning a single population with a known variance
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 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 professor gives an exam in which the mean score is 78 points. She gives another exam to test whether or not scores change. In this example, the null hypothesis is
mu = 78
A researcher reports a significant effect with t(14) = 3.24. Compute eta-squared for this result.
n= 0.43 (large effect size)
Computing a one-sample t test is appropriate when
participants are assigned to only one group the population variance is unknown participants are observed one time
The estimated standard error in the t statistic uses the ________ to estimate the ________ when the population variance is unknown.
sample variance; population variance
A professor finds that the average SAT score among all students attending his college is 1150±150 ( ). He polls his class of 25 students and finds that the average SAT score is 1200. Suppose he computes a one-sample z test at a .05 level of significance. What is his decision?
to reject the null hypothesis for an upper-tailed test, but to retain the null hypothesis for a two-tailed test
A researcher obtains z = 1.45 for a one-sample z test. What is the decision for this test at a .05 level of significance?
to retain the null hypothesis
Given the following values: u= 6.0, M = 7.6, n = 36, o = 6, conduct a one-sample z test at a .05 level of significance. For a one-tailed test, upper-tail critical, what is the decision?
to retain the null hypothesis
