one sample t-test
compare a sample mean to a population mean or reference value; t distribution of means
degrees of freedom for a one sample t-test
N-1
paired samples t-test (dependent)
compare mean difference of paired observations to no difference; t distribution of means
degrees of freedom for a paired samples t-test
N-1
independent samples t-test
compare means from two unrelated samples
degrees of freedom for independent samples t-test
N-2
3 assumptions
1. dependent variable is a scale measure
2. participants are randomly selected
3. comparison distribution is approximately normal in shape
The difference between the denominator in a z test and that of a single sample t test is...
in the z test we divide by the actual population standard error, but in a t test we divide by the sample standard error
as sample size gets larger, the t distributions get...
narrower
with very few degrees of freedom, the test statistic...
needs to be more extreme to reject the null hypothesis
appropriate APA format for a t statistic of 2.8 with degrees of freedom equal to 4 and p less than 0.05
t(4)=2.8, p<0.05
Why do we modify the formula for calculating standard deviation when using t tests? (and dividing by N-1)
We modify the formula to acknowledge the fact that there is likely to be some level of error when estimating the population standard deviation from a sample.
Explain why the standard error for the distribution of sample means is smaller than the standard deviation of sample scores
The distribution of sample means is always smaller than the distribution of sample scores because the effect of an extreme score is reduced when a mean is calculated based on many scores. Because of this, the standard error of the means is smaller than th
When is it appropriate to use a single-sample t test?
when we know the mean but not the standard deviation
one of the first steps in calculating the paired samples t test is...
creating a difference score for each pair in the sample
in a dependent samples t test, the null hypothesis posits that the mean of the comparison distribution is....
0
A study by Bettmann (2007) published in the Journal of the American Psychoanalytic Association assessed whether the attachment relationships between adolescents and their parents change as a result of a residential wilderness treatment experience for the
There will be no difference in attachment relationships after the wilderness experience.
A recent study investigated the possible effects of hair loss prevention drugs (e.g., Propecia) on men's sexual interest (libido). Suppose the researchers measured libido both before and after use of the drugs and reported these findings from a paired-sam
The researchers found that there was not a significant difference in libido after taking the drugs.
When calculating a confidence interval for a paired-samples t test, what value should be at the center?
sample mean difference
Other factors remaining constant, how does SM affect the width of a confidence interval?
if SM is larger then the confidence interval will be wider
Other things being equal, a larger sample size will _______ effect size.
have no effect on
How is the formula for Cohen's d for a paired-samples t test different from the d formula for the single-sample t test?
The mean and standard deviation are for difference scores rather than individual scores.
A calculated effect size of -0.75 for a paired-samples t test would tell us:
that the sample means are 0.75 standard deviation units apart
Which of the following designs would be most susceptible to order effects?
within-groups, before and after design
Your instructor decides to test the effectiveness of two different lecture techniques�multimedia vs. discussion�for her two sections of statistics. In one section she uses the multimedia technique during the first half of the semester and discussion for t
counterbalancing
When do we use a paired-samples t test?
We use a paired samples t test when comparing two means for a within-groups design. It can be used to analyze the data from many studies.
Why is the population mean almost always 0 in a paired-samples t test?
if population one and two are equal, then population two minus population one will equal zero. This means the mean of the comparison distribution will be zero.
If we calculate the confidence interval around the sample mean difference used for a paired-samples t test and it does not include the value of 0, what can we conclude?
that we will reject the null hypothesis
We introduced confounding variables (or confounds) in Chapter 1. Explain why order effects might be an example of a confound.
Order effects refer to how a participant's behavior chanted when a variable is presented a second time. This could be an example of a confound because participant's are likely to improve the second time around. Their behavior would be influenced by their