Lecture 7 - T-Tests

Question 1

Between-Subjects T-Test (Independent T-Test)

Answer 1

A test that uses the t-statistic to establish if two means obtained from independent samples differ significantly.

1. Calculate the descriptive statistics
2. Identify whether the data meet the assumptions of parametric statistics
3. Calculate the t value
4. Identify whether the result is significant (you need the critical value, degrees of freedom, alpha level, and one or two-tailed hypothesis)
5. Reject or Fail to Reject the Null-hypothesis
6. Write it up
   * t*(df)=t-value, p<0.05

Question 2

Within-Subjects T-Test (Paired/Dependent)

Answer 2

A test that uses the t-statistic to establish if two means obtained from two related samples differ significantly.

1. Calculate the descriptive statistics
2. Identify whether the data meet the assumptions of parametric statistics
3. Calculate the t value
4. Identify whether the result is significant (you need the critical value, degrees of freedom, alpha level, and one or two-tailed hypothesis)
5. Reject or Fail to Reject the Null-hypothesis
6. Write it up

t(df)=t-value, p<0.05

Question 3

Homogeneity of Variance

Answer 3

Similar variance across conditions. The largest standard deviation divided by the smallest should not be greater than 4.

Question 4

Degree of Freedom

Answer 4

The number of individual scores that can vary without changing the sample mean.

For independent t-test: df = (n1 - 1)+(n2 - 1)

For dependent t-test: df = n - 1

Question 5

Critical Value

Answer 5

The value of the test statistic for which the test just rejects the null hypothesis at the given significance level (test statistic value).

Question 6

Alpha Level

Answer 6

A prespecified cutoff point used to judge whether a result (our t-test) is statistically significant or not; in psychology, p<0.05.

Question 7

Critical Value Table

Answer 7

Used to calculate whether the test statistic is significant (if it is larger than the value in the table, it is significant).