Test 3.2 Flashcards
A study based on another study that uses different methods, a different manipulation, or a different measure.
conceptual replication
Repeating a study using the same means of manipulating and measuring the variables as in the original study.
exact replication
A study that varies from an original study in one systematic way- for example, by using a different number or type of subjects, a different setting, or more levels of the independent variable.
systematic replication
A parametric inferential statistical test of the null hypothesis for a single sample where the population variance is not known.
t-test
______ is a means of determining the number of standard deviation units a score is from the mean (µ) of a distribution.
t test
With a t test, the _________ is not known
population variance
The t test typically involves using smaller samples (N
30
The number of scores in a sample that are free to vary
degrees of freedom
_______= N-1
degrees of freedom (df)
When the sample size is large, the t distribution is the same as the z distribution.
True or False
True
If t = +2.06, it means that _____
our sample mean falls 2.06 standard deviations above the population mean.
A parametric inferential test for comparing sample means of two independent groups of scores.
independent-groups t test
Indicates whether the two samples perform so similarly that we conclude they are likely from the same population or whether they perform so differently that we conclude they represent two different populations.
independent-groups t test
The standard deviation of the sampling distribution of differences between the means of independent samples in a two-sample experiment
standard error of the difference between means
If t obt= 4.92 Spaced study has 10 people Massed study has 10 people a= .05 one tailed Ho: µ1≤µ2 Ha: µ1>µ2 do we reject of fail to reject the null hypothesis?
1-tailed test, so we have 18 degrees of freedom, we reject the null hypothesis, bc the critical t is 1.734, and so Our t obt is larger than the critical t and so we support the alternative hypothesis. The results are significant at the .05 level.
The results would be
t(18)=4.92, p
When a result is significant, the p value is reported as ______ .05.
less than
We want the probability to be ______.
small, because we want to be confident that there is only a small probability that our results were due to chance. This means it is highly probable that the observed difference between the groups is a meaningful difference and actually due to the IV.
We want the t score to be ______.
large to increase the chance that it will be significant.
What will increase the size of the tscore?
anything that increases the numerator or decreases the denominator in the equation.
What will increase the numerator?
a larger difference between the means for the two groups (a greater difference produced by the independent variable). This difference is somewhat difficult to influence. However, if we minimize chance in our study and the IV truly does have an effect, then the means should be different.
What will decrease the size of the denominator?
Because the denominator is the standard error of difference between the means and is derived by using s (the unbiased estimator of the population standard deviation), we can decrease by decreasing the variability within each condition or group or by increasing the sample size.
What three aspects can increase power?
- greater differences produced by the IV (increase numerator)
- less variability of raw scores in each condition (decrease denominator)
- increased sample size (decrease denominator)
In creating a graph, we place the _____ on the x-axis and the ____ on the y-axis.
IV on x-axis
DV on y-axis
the y-axis should be _____ of the length of the x-axis.
60-75%
The proportion of variance in the DV that is accounted for by the manipulation of the IV.
effect size
_______ indicated how large a role the conditions of the IV play in determining scores on the dependent variable.
effect size
The effect size is an estimate of the effect of the _______, regardless of sample size.
independent variable
The _____ the effect size, the more consistent is the influence of the independent variable.
larger
The greater the effect size, the more that knowing the conditions of the IV improves our accuracy in predicting subjects’ scores on the ________.
dependent variable
For the t test, one formula for effect size is ______ and another is .
cohen’s d
r^2
An inferential statistic for measuring effect size
cohen’s d
According to Cohen, a small effect size is one of at least _____, a medium effect size is at least _____, and a large effect size is at least a _____.
small 0.20
medium 0.50
large 0.80
___ measures the proportion of variance accounted for in the dependent variable based on knowing which treatment group the participants were assigned to for the independent variable.
R^2
for r^2, ___ is small, _____ is medium, _____ is large.
.01 is small, .09 is medium, .25 is large.
When finding a confidence interval, you always t cv for a ______.
two-tailed test
The 95% confidence interval of 2.92-7.28 (in the spaced/massed study example) means that if someone asked how large a difference study type makes on test performance, we could answer that we are 95% confident that the difference in performance on the 30-item test would be between _________.
2.92-7.28 correct answers.
One assumption of the independed-groups t test is that if we could compute the true variance of the population represented by each sample, the variances in each population would be the same, which is called ________.
homogeneity of variance
A parametic test for a two-group between-subjects design.
independent-groups t test
What does the independent-groups t test do?
compares performance of the two groups to determine whether they represent the same population or different populations
What are the 4 assumptions of the independent-groups t test?
- interval-ratio data
- normal distribution
- homogeneity of variance
- independent observations
How is effect size different from significance level? in other words, how is it possible to have a significant result yet a small effect size?
Effect size indicates the magnitude of the influence of the experimental treatment, regardless of the sample size. A result can be statistically significant because the sample size is very large, even if the effect of the IV is not so large. Effect size indicates whether this is the case because, in this situation, effect size should be small.
How does increasing the sample size affect a t test?
In the long run, it means that the obtained t is more likely to be significant. In terms of the formula used to calculate t, increasing the sample size will decrease the standard error of the difference between means (sx1-x2). This, in turn, will increase the size of the obtained t. A larger obtained t means that the obtained value is more likely to exceed the critical value and be significant.
How does decreasing variability affect a t test?
Decreasing variability also makes a t test more powerful (likely to be significant) because decreasing variability also means that sx1-x2 (standard error of the difference between means ) will be smaller. Again, this increases the size of the obtained t, and a larger obtained t means that the obtained value is more likely to exceed the critical value and be significant.
An experiment in which different subjects are assigned to each group is a ______.
between-subjects
When we use ____, we randomly determine who serves in each group in an experiment.
random assignment
When the DV is measured both before and after manipulation of the IV, we are using a ______ design.
pretest/posttest control group
_______ is the extent to which the results of an experiment can be attributed to the manipulation of the IV, rather than to some confounding variable.
internal validity
The extent to which the results of an experiment can be generalized is called_____.
external validity
A(n) ______ is a parametric inferential test for comparing sample means of two independent groups of scores.
independent-groups t test
_______ is an inferential statistic for measuring effect size with t tests.
cohen’s d
If we were to conduct a replication in which we increased the number of levels of the IV, we would be using a _____ replication.
systematic
The value of the t test will _____ as sample variance decreases.
increase
which of the following t test results has the greatest chance of statistical significance?
a. t(28) = 3.12
b. t(14) = 3.12
c. t(18) = 3.12
d. t(10) = 3.12
a. t(28) = 3.12
If the null hypothesis is false, then the t test should be ______.
greater than 1
Imagine that you conducted an independent groups t test with 10 participants in each group. For a one-tailed test, the tcv at a=.05 would be:
±1.734
If a researcher reported for an independent-groups t test that t(26) = 2.90, p
28
Cohen’s d is a measure of ___ for a ____.
effect size; t test
tcv = ±2.15 and tobv =-2.20. Based on these results we:
reject Ho
