What it does: The One-Sample T Test compares the mean score of a sample to a known value. Usually, the known value is a population mean.

Where to find it: Under the Analyze menu, choose Compare Means, then One-Sample T Test. Move the dependent variable into the "Test Variables" box. Type in the value you wish to compare your sample to in the box called "Test Value."

Assumption:
-The dependent variable is normally distributed. You can check for normal distribution with a Q-Q plot.

Hypotheses:
Null: There is no significant difference between the sample mean and the population mean.
Alternate: There is a significant difference between the sample mean and the population mean.

SPSS Output

Following is a sample output of a one-sample T test. We compared the mean level of self-esteem for our sample of Wellesley college students to a known population value of 3.9

First, we see the descriptive statistics.

The mean of our sample is 4.04, which is slightly higher than our population mean of 3.9.

Next, we see the results of our one-sample T test:

Our T value is 2.288.

We have 112 degrees of freedom.

Our significance value is .024.

There is a significant difference between the two groups (the significance is less than .05).

Therefore, we can say that our sample mean of 4.04 is significantly greater than the population mean of 3.9.

Home | Review Test | Decision Tree | Procedure List

Susan Archambault
Psychology Department, Wellesley College

Created By: Nina Schloesser '02
Created On: July 30, 2000
Last Modified: July 30, 2000