Using SPSS and PASW/Descriptives
Descriptive statistics are used to describe variables. Examples of descriptive statistics include: mean, median, mode, standard deviation, and range. In this chapter you'll learn how to have SPSS calculate three descriptive statistics for you: the mean, median and mode.
In order to generate descriptives in SPSS, you first need to open up a data set. In this case we are going to use the Genetic Counseling example data set. The variable we'll use to illustrate descriptive statistical analysis is “age.”
To calculate descriptives in SPSS, click “Analyze” → “Descriptive Statistics” → “Frequencies.”
Once you click on Frequencies, a Frequencies Window will appear on the screen. Find the variable labeled “age” and click the blue arrow to move it over into the Variable Box.
Once you have done this, click on the tab that is labeled Statistics. A new window will appear. In this window, select mean, median, and mode then click “Continue.”
Once the box disappears, click “OK” in the Frequencies Box and the mean, median, and mode, for the age of participants should appear in the Output window.
In the example above, the mean (average) age of participants is 35.93. The median, or middle number in the data set is 33, and the mode or the most commonly occurring age of participants in this study is 28.
Distribution Curves in SPSS
If you want to see where the mean, median, and mode fall on a frequency distribution curve, SPSS can do this for you. This is useful when you are trying to determine if the curve is normal or skewed. Skewness statistics are used to determine whether sample data are so skewed that they suggest that the population scores are skewed (a detailed discussion of skewness statistics is beyond the scope of this book). We are going to continue with the above example with using the variable of “age.”
First, repeat all of the above steps when you were finding the mean, median, and mode. When you have the “Frequencies” window open, click the tab that is labeled “Charts.”
Now select the radio button that says “Histograms” and choose “With Normal Curve.” Click “Continue” then “OK,” and your chart should pop up in the Output box:
The frequency curve in this example shows that the mean (35.9), median (33), and mode (28), create a positively skewed distribution (meaning some very large values in a positive or higher direction).
Chapter 15 contributed by Kristin Mraz.