A professor is interested in the effect of dressing informally on students' ratings of her. For previous courses her average ratings were 3.25, but the SD is unknown. During the first half of this semester, she dressed casually. She gave her 30 students a mid-term evaluation and found that her average rating was 3.14. After the mid-term evaluation, she started dressing up for class. At the end of the semester, she received an evaluation rating of 4.25.

To determine whether dressing casually hurts her evaluation (i.e., comparing whether her mid-term evaluation is different from her general evaluation from previous courses), she would use:

z test for independent samples test

t-test for independent samples

t-test for dependent sample

t-test for single sample