You always begin by defining a set of

*variables**,*and then you enter data for the variables to create a number of

*cases.*For example, if you are doing an analysis of automobiles, each car in your study would be a case. The variables that define the cases could be things such as the year of manufacture, horsepower, and cubic inches of displacement. Each car in the study is defined as a single case, and each case is defined as a set of values assigned to the collection of variables. Every case has a value for each variable. Variables have types. That is, each variable is defined as containing a specific kind of number. For example, a

*scale**variable is a numeric measurement, such as weight or miles per gallon. A*

*categorical**variable contains values that define a category; for example, a variable named gender could be a categorical variable defined to contain only values 1 for female and 2 for male. Things that make sense for one type of variable don’t necessarily make sense for another. For example, it makes sense to calculate the average miles per gallon, but not the average gender.*

After your data is entered into SPSS
— your cases are all defined by values stored in the variables — you can run an
analysis. You have already finished the hard part. Running an analysis on the
data is much easier than entering the data. To run an analysis, you select the
one you want to run from the menu, select appropriate variables, and click the
OK button. SPSS reads through all your cases, performs the analysis, and
presents you with the output.

You can instruct SPSS to draw graphs
and charts the same way you instruct it to do an analysis. You select the
desired graph from the menu, assign variables to it, and click OK. When
preparing SPSS to run an analysis or draw a graph, the OK button is unavailable
until you have made all the choices necessary to produce output. Not only does
SPSS require that you select a sufficient number of variables to produce
output, it also requires that you choose the right kinds of variables. If a
categorical variable is required for a certain slot, SPSS will not allow you to
choose any other kind. Whether the output makes sense is up to you and your
data, but SPSS makes certain that the choices you make can be used to produce
some kind of result.

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