A quick review of steps for Z-scores testing in
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quick review of steps for Z-scores testing in SPSS
- Enter your data into the first column
of the data file.
- 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.
- Save the data file to a meaningful
place with a meaningful name. This file should have a .sav extension.
- Click Analyze, Descriptive Statistics
and then Descriptives. A Descriptives box will appear.
- Move your variable to the Variable
box by clicking on it to highlight it and clicking on the arrow button.
- Check the “Save standard values as
variables,” option by clicking in the corresponding box.
- Click OK and wait a few seconds for
processing. The output will appear.
- 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.
- 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.
- Look in your data file, NOT your
- 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.
- 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.
- 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.
- 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.
- Report the type of tests used and
what they were used to test.
- Report the values for the raw score
and z-scores that you are interested in.
- Report your results in words that
people can understand.
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