A Z-score is a statistical tool that describes how many standard deviations a data point lies from the average in a given set of data. The Z-score may also be called the standard score, Z-value, normal score or the standardized variable. Calculating a Z-score by hand is a long and difficult process. Luckily, graphing calculators provide a quick way to calculate the Z-score.
Instructions
1. Determine the area "p" for which you would like to calculate the z-score. "P" represents the percentage of data that lies below the Z-score. For example, if you choose p = 70 percent and calculate a Z-score of 0.8, you can say that 70 percent of your data lies within 0.8 standard deviations from the mean.
2. Press the "2nd" key on your graphing calculator. You will notice that every key on your calculator has large text on the button (the primary menu) and smaller text above the button (the secondary menu). By pressing this key, you activate the secondary menu.
3. Press the "VARS" key, which has the secondary "DISTR" menu printed above it. Your screen will display the distribution menu.
4. Click the down arrow to select "3: invNorm(" on the menu. Press "Enter."
5. Type the "p" value that you determined in Step 1 as a decimal. For example, if you decided on p = 70 percent, type 0.7. Press "Enter." The graphing calculator will return the Z-value.
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