Psych Statistics - Module 5 Test
A study has 18 participants in the experimental group and 7 participants in the control group. What is the harmonic mean of these sample sizes?
(2)(18)(7)/(18 + 7) = 10.08
Suppose you carry out a study using a t test for independent means. The number of participants in each group is 50 and you conduct a **two-tailed test**. What would be the approximate level of power if you anticipated a **small effect size**? (Consult the power table 9-4.)
.17
Cohen's conventions for the t test for independent means are approximately __________ for a small effect size, __________ for a medium effect size, and __________ for a large effect size.
.2, .5, .8
Suppose you carry out a study using a t test for independent means. The number of participants in each group is 40 and you conduct a one-tailed test. What would be the approximate level of power if you anticipated a medium effect size? (Consult the power table 9-4.)
.72
Consider a study in which the population variance estimate based on an experimental group of 10 participants is 70, and the population variance estimate based on a control group of 20 participants is 50. Compute the pooled estimate of population variance.
56.4
Which of the following is an example of a situation in which you could conduct a t test for independent means?
A comparison of scores of participants in a memory study in which one group learns the words in alphabetical order and another group learns the words in order of word length.
In an experiment involving 50 participants, which study would have the most power?
A study with 25 in the experimental group and 25 in the control group
Each of the following is part of conducting a t test for independent means, EXCEPT:
difference scores are found for each participant
The comparison distribution for a t test for independent means is a:
distribution of differences between means
In a t test for independent means, when the number of scores in the two groups differs, the __________ is used as the equivalent of each group's sample size when determining power.
harmonic mean
When conducting a t test for independent means, a typical research hypothesis might be:
the mean of Population 1 is greater than the mean of Population 2
The comparison distribution for a t test for independent means is a t distribution (as opposed to a normal curve) because:
the population variance is estimated
In the formula"S2Difference= S2M1 + S2M2" the "S2M1" is:
the variance of the distribution of means for Population 1, based on an estimate of the population variance
For a study using a t test for independent means, the approximate number of participants needed for 80% power for an estimated large effect size and using a two-tailed test is:
26
For a study using a t test for independent means, the approximate number of participants needed for **80% power** for an estimated **small effect size and using a one-tailed test is**:
310
Which of the following is the MOST serious violation of an assumption for the t test for independent means?
The populations are dramatically skewed in opposite directions.
A research article based on a t test for independent means reports a result as "t(28) = 4.21, p < .01."
a. There were 30 participants in the study. b. The result was statistically significant. c. The t score was 4.21. **d. All of the Above**
When conducting a t test for independent means:
b. you assume the medians of the two populations are equal c. you reject the null hypothesis if the t score is more extreme than the cutoff t score d. all of the above
Many computer programs provide two sets of results for the t test for independent means. The standard method assumes that the population variances are __________ ; an alternative procedure takes into account that the population variances may be __________.
equal; unequal
In a t test for independent means, the weighted average of the estimates of the population variance from two samples is known as the:
pooled estimate of population variance
The effect size for the t test for independent means is the difference between the sample means divided by the:
pooled estimate of the population SD
A researcher hypothesizes that people of personality type K score higher than people of personality type R on an intelligence test. The SDifference turned out to be .9, while the mean score of type K people was 18.8 and the mean score for type R people was 21.3. What is the t score?
t = (18.8-21.3) / .9 = -2.78
Based on the following results, which would be the correct use of the formula t = (M1-M2) /SDifference?Sample 1: Mean = 60; Variance of the distribution of means = 2.Sample 2: Mean = 50; Variance of the distribution of means = 7.
t = 60-50 / 3
The __________ is a hypothesis-testing procedure in which there are two separate groups of people tested and the population variance is not known.
t test for independent means
Which of the following is an example of the most common way for a t test for independent means to be reported in a research article?
t(45) = 3.52, p < .05
A "distribution of differences between means" can be thought of as a distribution of as:
the differences you get when you repeatedly draw a sample mean from one population and a sample mean from another population and subtract one mean from the other
You conduct a t test for independent means and reject the null hypothesis. This means that:
the mean of one sample is so far from the mean of the other sample that you decide the samples must come from populations with different means
In the formula [t = M1-M2 /SDifference], "SDifference" is:
the standard deviation of the distribution of differences between means
The variance of a distribution of differences between means equals:
the sum of the variances of the two distributions of means
One of the assumptions for the t test for independent means is that:
the variance of each of the two parent populations is the same
When conducting a t test for independent means, once the variances are known for each of the distributions of means, the variances can be added together to give the:
variance of the distribution of differences between means
