Testing for differences Flashcards
What are some parametric tests?
Paired t-test
two-sample test
one-sample test
What are some non-parametric tests?
Mann whitney U
wicoxon
one-sample sign test
What is the quantifying difference?
Cohen’s d
what is the purpose of parametric T-tests?
testing for differences
hypotheses testing
can be one or two tailed tests
What are the assumptions of the T-tests?
continuous data
follows a normal distribution
variances are constant (standard deviations)
What happens in the assumptions of a T-test dont hold?
the statistical test is in doubt and the p-value may be wrong
Robust test can withstand some deviation
try to transform the data
Use a non-parametric test instead
When would you use the one sample t-test?
used to determine if mean of a sample is difference from an expected value
When would you use a paired t-test?
test for differences between two sets of paired observations
When would you used the two-sample t-test?
test whether the means of two independent sets of measurements are different
What are the assumptions of the paired t-test?
check that appropriate t-test assumptions are met.
What is the null hypothesis of the paired t-test?
The mean change or difference is zero
What is the rationale of the paired t-test?
calculate the difference between each pair of points, then determine if the mean of these values is different from zero
What is the method of using the paired t-test?
– Calculate the difference (d) between each pair of measurements
– Calculate the mean difference and standard error – Calculate the test statistic (|t|) and compare to the critical value
How do you interpret results compared to the critical value for the paired t-test?
– If |t| ≥ critical value, the null hypothesis is rejected, concluding the mean difference is “significantly” different from zero
– If |t| < critical value, there is not enough evidence to reject the null hypothesis, concluding the mean difference is not significantly different from zero
What are the assumptions of the two-sample t-test?
check appropriate t-test assumptions are met
samples are independent of each other
what is the null hypothesis to the two-sample t-test?
the difference between the two means is zero
What is the rationale with the two-sample t-test?
it compares the means from two independent samples, if the samples are not independent then the test will not be valid.
what is the null hypothesis for the one-sample t-test?
There is no difference between the sample population mean and an expected (given) value
What is the rationale for the one-sample t-test?
The test calculates how many standard errors the sample mean is away from the expected value (E)
How do you interpret the results for the one sample t-test?
The further away the mean is from the expected value, the larger the value of t, and the less probable it is
• The value of t can be positive or negative, it is the absolute value |t| of the difference that counts
• If |t| >critical value, then the difference is statistically significant
What is Cohen’s d looking at?
an effect size measurement that tells us the magnitude of an experimental treatment.
how do you calculate Cohen’s d?
𝑑 = (𝑀𝑔𝑟𝑜𝑢𝑝1−𝑀𝑔𝑟𝑜𝑢𝑝2) / 𝑆𝐷𝑝𝑜𝑜𝑙𝑒d
What are the results of cohens d?
d = 1, then groups’ means differ by 1 SD d = 0.5, the means differ by half an SD d = 2, means differ by 2 SDs
How do you interpret cohens d?
d <0.2, difference is minor, even if significant
d = 0.2, considered a “small” effect size
d = 0.5, considered a “medium” effect size
d = 0.8, considered a “large” effect size
