Research Chapter 11
If there is no difference between the distributions of scores in two groups, what is the effect size equal to?
0
What is the most common level of significance used in testing in the social sciences?
0.05
What is a small effect for Cohen's d?
0.17
If the number of participants in Group 1 = 54 and the number in Group 2 = 58, what is the associated degrees of freedom?
110
If the number of participants in Group 1 = 32 and the number in Group 2 = 30, what is the associated degrees of freedom?
60
Under what conditions would a researcher choose to use a t test for independent samples?
A researcher would choose the t test for independent samples if he or she were examining mean differences between two groups and if different subjects were in each group.
If the obtained value is less than the critical value, what should you do?
Accept the null hypothesis.
A researcher is testing a two-tailed null hypothesis at the p < 0.01 level with df = 48. What critical value would she or he use? Justify your answer.
Because there is no value for 48 degrees of freedom, the researcher could choose a critical value of 2.690, which corresponds with df = 45. This value would be a conservative value because it is the one obtained assuming a smaller sample size than the researcher actually has.—OR—Because there is no value for 48 degrees of freedom, the researcher could choose a critical value of 2.678, which corresponds with df = 50. Although this value is closer to the actual sample size, it is important to recognize that this critical value would be considered more liberal. (It is based on a larger sample size than the researcher actually has.)
In the effect size formula, what does ES stand for?
Effect size
True/False: Effect size is a value that approximates the sample size and is a component of many statistical tests.
False
True/False: The sign of the observed t value (i.e., whether it is positive or negative) is a crucial element in conducting the t test for independent samples.
False
True/False: The test for independent samples should be used when participants are tested multiple times.
False
The null hypothesis in an independent-samples t-test would be represented as follows:
H0: μ1 = μ2
The research hypothesis in an independent-samples t-test would be represented as follows:
H1: 1 >2
What does t(47) = 0.23 mean?
In the above statement, t represents the test statistic used (t test) while 47 is the degrees of freedom. The value 0.23 is the statistic value or obtained value for the t test.
If the obtained t value is 7.14, and the critical value is 6.10, what decision should be made?
Reject the null hypothesis.
When the obtained value is greater than the critical value, what should you do?
Reject the null hypothesis.
The t test for independent samples assumes which of the following?
Scores are independent.
In the effect size formula, what does s stand for?
Standard deviation
What does the symbol t represent in the following: t(42) = 5.15, p < 0.01?
Test statistic
Under what circumstances would a researcher reject the null hypothesis?
The null hypothesis is rejected if the obtained value is greater than the critical value.
What is the simplest way to compute an effect size?
The simplest way to compute an effect size is to divide the difference between the means by any one of the standard deviations.
True/False: A larger effect size represents a greater difference between the two groups.
True
True/False: A t test is conducted to detect differences between two groups in which participants are tested only once.
True
True/False: Effect size is the magnitude of the differences between groups.
True
True/False: Pooled standard deviation, part of the formula for the Cohen's d effect size, is similar to an average of the standard deviations from both groups.
True
True/False: The homogeneity-of-variance, an assumption underlying the t test, states that the amount of variability in both groups is equal.
True
How many groups are involved in the t test for independent samples?
Two
Why do we calculate effect size?
We calculate effect size to determine the magnitude of the treatment, or how different the two groups are from one another.
If you have a sample size of 500, should you interpret the statistical significance or the effect size?
With a small sample size, you could interpret either, but with a large sample size, the effect size will let you know if the significance is due to your treatment effect or due to the power of your test.
What are you assuming when you use the simple formula for effect size?
You are assuming that the standard deviations between the groups are equal to one another.
A researcher wants to study the impact of pizza consumption on the happiness of college freshmen, sophomores, and juniors. What test statistic would the researcher need to use to evaluate the difference in effectiveness between the groups?
analysis of variance
To examine the difference among the average scores of three unrelated groups, which of the following statistical techniques should be selected?
analysis of variance
The SPSS output for an independent-samples t-test includes all but which of the following?
correlation coefficient
In order to determine whether you will reject the null hypothesis, the test statistic must be compared against the ______.
critical value
In order to compute the test statistic, or t value, you must first approximate the sample size by calculating the ______.
degrees of freedom
What does the number 42 represent in the following: t(42) = 5.15, p < 0.01?
degrees of freedom
What does the number 58 represent in the following: t(58) = 2.001, p < 0.05?
degrees of freedom
A measure of the magnitude of the difference between two groups is _____.
effect size
Based on the equation: t(42) = 5.15, p < 0.01, what is the right choice in the following?
group 1= 22; group 2= 22
The term for the assumption that the amount of variability in each of the two groups is equal is ______.
homogeneity of variance
A researcher wants to create an intervention to improve the well-being of first-semester graduate students, so she gives the professional school counseling students specific doses of rocky road ice cream and the mental health counseling students specific doses of licorice. To analyze the differences in well-being, she would use a(n) ______.
independent-samples t test
Please identify the elements of the formula for an independent-means t test.
is the mean for Group 1. is the mean for Group 2. n1 is the number of participants in Group 1. n2 is the number of participants in Group 2. s12 is the variance for Group 1. s22 is the variance of Group 2.
If the effect size is 0.37, what is your interpretation of the group difference?
medium
If there is a significant difference between the distributions of scores in two groups with effect size at .37, how big are the differences between the two groups?
medium
Which of the following is the formula used to calculate degrees of freedom for a t test?
n1 - 1 + n2 - 1
In the t test for independent samples, the actual statistical test is ______.
nondirectional
When computing effect size, the sample size is ______.
not considered
Independent groups are ______.
not related in any way
In the formula that computes a t value, what does n1 represent?
number of participants for Group 1
The test statistic calculated by the statistical procedure selected is known as the ______.
obtained value
What is the t statistic value also known as?
obtained value
When examining group difference where the direction of the difference is specified, which of the following is used?
one-tailed test
The t test for independent means is used when each group is tested ______.
only once
The t test for independent means is used when you are testing how many groups?
only two groups in total
What does the symbol p represent in the following: t(42) = 5.15, p < 0.01?
probability
When it comes to significance testing, the level of risk is ______.
set by the researcher
What does the number 0.01 represent in the following: t(42) = 5.15, p < 0.01?
significance level
What does the number 0.05 represent in the following: t(58) = 2.001, p < 0.05?
significance level
What does the number 2.001 represent in the following: t(58) = 2.001, p < 0.05?
t value
What does the number 5.15 represent in the following: t(42) = 5.15, p < 0.01?
t value
What does the letter t represent in the following: t(58) = 2.001, p < 0.05?
test statistic
In the effect size formula, what does X1 bar stand for?
the mean for Group 1
In the formula that computes a t value, what does represent?
the mean for Group 1
True/False: There is an important difference between a significant result and a meaningful result.
true
When examining group difference where no direction of the difference is specified, which of the following is used?
two-tailed test
The t test for independent means is used when looking at the difference in average scores of one or more variables between ______ group(s) that are ______ one another.
two; independent of
In the formula that computes a t value, what does s12 represent?
variance for Group 1
Which of the following is a major assumption of the t test regarding the amount of variability in each group?
variances are equal
