Studied by 2 people
Dependent (paired t-test)
2 samples are related, typically that the 2 samples come from the same person measured twice
What question does a paired t-test answer?
are the differences in the scores on average significantly different from zero
Conditions for paired t-test
both groups will have the same number of responses since the scores for each response are matched -can't have missing data
sample size for paired t-test
the number of paired values (half the number of total responses)
null hypothesis for paired t test
mean of the difference is equal to zero
assumptions for paired t-test
-random sampling -independent observations -normal population distribution or large sample (25+)
alpha level
.05
standard deviation
sqrt(sum of differences between observed and average difference of scores)/n-1
independent t-test
comparing 2 groups of unrelated responses to see if the group means are significantly different
how are independent t-tests different from paired t-tests?
independent t-test involves 2 entirely separate groups
assumptions of independent t-test
-random samples -independent observations -normal population distribution or large sample -independent samples
paired t-test alternate hypothesis
mean of differences does not equal zero
null hypothesis for independent t test
(mean of group one)-(mean of group 2)=0
alternate hypothesis for independent t-test
(mean of group one)-(mean of group 2) does not equal zero
degrees of freedom of independent t test
smaller sample size minus one
bar chart of means
error bars are based on standard error -if bars overlap there is no significant difference -if they do not overlap there is a significant difference
when writing hypothesis notation for independent t test
the order which you subtract the two group means does not matter as long as it's the same way calculated during t test
When to reject the null hypothesis
When the t-stat is more extreme than the t-critical
When to fail to reject the null hypothesis
when the t-stat falls between the t-critical values
degrees of freedom of paired t-test
population size minus 1
