Psychology 231

SPSS – One-Sample T-Test

The data example – On a standardized spatial skills task, normative data reveal that people typically get m = 15 correct solutions.  A psychologist tests n = 7 individuals who have brain injuries in the right cerebral hemisphere.  For the following data, determine whether or not right-hemisphere damage results in significantly different performance on the spatial skills task.  Test with alpha of .05 and two tails. The data are: 12, 16, 9, 8, 10, 17, 10.

STEP 1: Define variable name, label, and values

Open SPSS and choose Type in data. Start by naming the variable of interest. Click the Variable View sheet tab.  Type the variable name (8 characters max) in the Name column (e.g., Score). If needed, specify variable type, width, and number of decimals or simply accept the default settings. You have the option of typing a more descriptive variable name (255 characters max) in the Label column.  There is no need to specify values for this analysis.

 

STEP 2: Input the data into SPSS

      Make sure to click back into Data View.  Enter all scores in a single column beneath the variable name (Score).

 

STEP 3: Select the statistical procedures

Go to the Analyze menu and select Compare Means and then select One-Sample T-Test.

 

STEP 4: Select the variables

Inside the subcommand box, select the variable column to analyze (Score, for example) by using the arrow keys to move the variable name into the right box.  To specify the test value, click in the box and type the value of m if Ho is true.  For the current example, type 15.  Click the OK button.

 

STEP 5: Look up the t-statistic (p. 693) and make a decision regarding Ho.  For a two-tailed test with alpha set at .05 and df = 6, the critical value of t = + or – 2.447.  Our calculated value of –2.485 falls within the critical region, so we reject Ho.  Shortcut:  The data output lists Sig. (2 tailed) at .047, which is less than .05, so we reject Ho. To get the significance level for a 1-tailed test, divide the provided 2-tailed probability by 2.