m38 problem set STATISTICS

SPSS and Descriptive Statistics

Descriptive statistics are statistics that describe a variable’s central tendency (the ‘middle’ or expected value) and dispersion (the distribution of the variable’s responses). Be aware that SPSS will calculate statistics even if the measure of central tendency and dispersion are not appropriate. What do I mean by inappropriate descriptive statistics? Let's think about the variable GENDER. Most often, you will find two alternatives for this variable: male or female. (Whether or not this is exhaustive is another discussion). Assume you have 25 people in your dataset: 15 have identified as male, 10 identifed as female. Does it make sense to use a mean for this? No, not at all in our society. Nominal variables are simply an identity or a yes/no variable, and an average makes no logical sense.

 

As a reminder, I’ve included the basic statistics that are appropriate for different types of variables:

 

Discrete variables:                  Mode, Median

Continuous variables:             Median, Mean Range, Interquartile Range, Variance, Standard Deviation

 

Nominal:                                  Mode

Ordinal:                                   Median, Range, Interquartile Range

Interval or Ratio:                     Mean, Range, Interquartile Range, Variance, Standard Deviation

 

 

Let’s use the variable ‘happy’ again. Begin just like you did when you were going to calculate frequency (this is in the previous content guide). Once you have clicked selected Analyze, then Descriptive Statistics and Frequencies, you will have this screen again:

Before selecting ‘OK’, click on the “statistics” button. This is the place that you can select the appropriate statistics. Since happy is an ordinal variable, let’s select median and range. Your screen should look like this:

Now click Continue and then OK. Your screen will look like this:

 

 

 What does this output mean? You already know how to read the frequency chart. The only change is in the statistics chart. You have a median of 2 and that there was a range of 2 around the median.

 

HINT: Make sure that you always check your statistics when you change your variable. SPSS will not make the change for you!!