Research Skills: Week 89

THE T-TEST

Learn
The t-test provides the probability that the null hypothesis is true when examining the difference between the means of two groups. Normally we use this test when data sets are small. There are two different t-tests

Unlearn
However there are two different type of t-test called the “paired samples t-test,” and the “independent samples t-test”. Therefore we will use t-test depending on the situation.

Relearn
THE PAIRED SAMPLES T-TEST
When do we use it? We assume that the confidence interval is at 95% all the time.
1. When there is a natural relationship between the subjects from whom the two sets of scores are obtained.
Example 1: Looking at differences between pre- and post-tests of one group, you would choose the paired samples t-test, the scores of both data sets came from the same persons.
Example 2: A teacher diagnostically tests her students at the beginning of the year. After intensive instruction, the test is repeated at the end of the semester. She is interested in knowing if the students have made significant gains.

THE INDEPENDENT SAMPLES T-TEST
(We use this t-test more often) When do we use it?
When there is no natural relationship between subjects whose scores are being contrasted. Comparing scores obtained from two different groups of people, you would use this t-test.
The data descriptions are normally distributed and of the groups are homogeneous.
Example 1: Two groups of students are identified: an experimental and a control group. Both groups are pretested (Both groups are posttested), an intervention is used with the experimental group and is withheld from the control group. Both groups are posttested.
Example 2: TLI scores are collected on students who have attended school using block scheduling and students who have attended schools with traditional scheduling. We want to know if the TLI scores are significantly different according to the schedule experienced by the students. (We reject the null when p<0.05;>0.05).