A quick review of steps for independent samples T-tests

Home > A quick review of steps for independent samples T-tests







Background | Enter Data | Analyze Data | Interpret Data | Report Data

I. Enter your data into two columns in the data file

 

  1. Use the first column of the data file to show SPSS the difference between your two conditions. Use two different numbers to represent each of your two conditions. For example, use 1s to represent the first condition and 2s to represent the second condition.
  2. Give the first column of data a meaningful name. It’s a good idea to use the letters “IV” in this name.
  3. Use the second column of the data file to type the data collected for each participant in each condition. Make sure that data for the first condition goes next to the numbers that you used to represent the first condition in the first column. Similarly, make sure that the data for the second condition goes next to the numbers that you used to represent the second condition in the first column.
  4. Give the second column of data a meaningful name. It’s a good idea to use the letters “DV” in this name.
  5. Save the data file to a meaningful place with a meaningful name. This file should have a .sav extension.

II. Analyze your data

 

  1. Click Analyze, Compare Means and then Independent Samples T Test. An Independent Samples T Test box will appear.
  2. Move your IV to the Grouping Variable box by highlighting it and clicking on the corresponding arrow.
  3. Click the Define Groups button. A Define Groups box will appear.
  4. Define the conditions of your experiment by telling SPSS the numbers you used to represent the first and second condition of your experiment.
  5. Click Continue. The Define Groups box will disappear and you will be back to the Independent Samples T Test box.
  6. Move your DV into the Test Variables box by highlighting it and clicking on the corresponding arrow.
  7. Click OK and wait a few seconds for processing.
  8. Save the output to a meaningful place with a meaningful name. SPSS should give the output file a .spo extension.

 

III. Interpret your results

 

  1. Look in the Group Statistics box for condition means, standard deviations and number of participants.
  2. Make sure the number of participants for each condition is accurate. If it is not, go back to the data file and make sure it is correct.
  3. Look in the Independent Samples Test box.
  4. Determine which of the two rows to read from by checking the Sig. value in the Levene’s Test for Equality of Variances column. If the Sig. value is greater than .05, read from the top row. If the Sig. value is less than or equal to .05, read from the bottom row.
  5. Check the Sig (2-Tailed) value in the appropriate row to determine if there was a statistically significant difference between group means. If the Sig (2-Tailed) value is greater than .05,  you can conclude that there is no statistically significant difference between your two conditions – that the IV did not have a significant effect on the DV. However, if the Sig (2-Tailed) value is less than or equal to .05, you can conclude that there is a statistically significant difference between your two conditions. This means that it is likely that the IV did have an effect on the DV and the results were not likely due to chance.

 

IV. Report your results

 

  1. Report the type of test used and what it was used to test.
  2. Report whether or not there was a significant difference between your conditions. Include the group means, standard deviation, and the T-test values.
  3. Report your results in words that people can understand.

 

Background | Enter Data | Analyze Data | Interpret Data | Report Data


 

 

 

 

 

 

 

Home | Copyright 2008 | Tell a Friend