A quick review of steps for Z-scores testing in SPSS

Home > A quick review of steps for Z-scores testing in SPSS

 

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

I. Enter your data into the first column in the data file

 

  1. Enter your data into the first column of the data file.
  2. Give the first column of data a meaningful name by double clicking on the top of the column. Fill in the ‘variable name’ in the Define Variable box and Click OK. 
  3. 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, Descriptive Statistics and then Descriptives. A Descriptives box will appear.
  2. Move your variable to the Variable box by clicking on it to highlight it and clicking on the arrow button.
  3. Check the “Save standard values as variables,” option by clicking in the corresponding box.
  4. Click OK and wait a few seconds for processing. The output will appear.
  5. You might want to write down the mean in the output file. You can optionally save the output to a meaningful place with a meaningful name. SPSS should give the output file a .spo extension.
  6. Your z-scores will be in your data file. Go back to the data file and save it again, now that it has been modified by SPSS. The data file will still have a .sav extension.

 

III. Interpret your results

 

  1. Look in your data file, NOT your output file.
  2. Your z-scores will appear in a second column of data with the letter ‘z’ in front of its name. Each data point that you entered in the column on the left will have a corresponding z-score printed in the column just next to it.
  3. If a z-score is positive, its’ corresponding raw score is above (greater than) the mean. If a z-score is negative, its’ corresponding raw score is below (less than) the mean.
  4. The absolute value of a z-score will tell you how far away the score is from the mean in standard deviation units. 95% of scores are going to be no more than 2 standard deviation units away from the mean. That means that most scores will fall between z=-2 to z=+2. However, some scores will be greater than the absolute value of 2. You can interpret these scores to be very far from the mean.
  5. If A z-score…
  • Has a value of 0, it is equal to the group mean.

  • Is positive, it is above the group mean.

  • Is negative, it is below the group mean.

  • Is equal to +1, it is 1 Standard Deviation above the mean.

  • Is equal to +2, it is 2 Standard Deviations above the mean.

  • Is equal to -1, it is 1 Standard Deviation below the mean.

  • Is equal to -2, it is 2 Standard Deviations below the mean.

IV. Report your results

 

  1. Report the type of tests used and what they were used to test.
  2. Report the values for the raw score and z-scores that you are interested in. 
  3. Report your results in words that people can understand.


 

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


 

 

 

 

 

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