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Compute Function
(recoding) Task: Using the Computer Function to recode a
reverse coded item.
Start off by importing the
ex3reverse.sav into the Data Editor window of PASW / SPSS (from this
point forward referred to as simply SPSS).
The compute function can be used to recode a Likert scale item which was
initial reverse coded by the wording of its stem or statement. The keys to using
compute to recode an item are two simple formulas. The general idea is that we
add 1 to the number of possible response choices, creating a constant, and then
subtract the old value from that constant.
Formula (1): k + 1 = C
where k equals the number of possible Likert response choices
and C equals the Constant we will apply in the compute function.
Formula (2): C - O = RC
where C equals the Constant from the previous equation, O
equals the old variable values, and RC equals the newly recoded variable
values.
For instance, our current example uses a 5-point Likert response format.
Since we want to reverse the numeric coding in our data file, we add 1 to 5 and
get 6 as our constant.
(1): 5 + 1 = 6
We then subtract each person's response on the old variable from 6 and the
result will be each person's recoded response.
(2): 6 - q4 = q4_RC
For the example below, we will be recoding question 4 (q4) as was done using
the Recode function in a previous module (Module
4.3). If you would like a more detailed description of our example data and
the fictional situation behind it, please review that module.
To use the Compute function, simply go to "Transform", "Compute Variable..."
You should now see the "Compute Variable" dialog box.
In the Compute dialog, first type q4_RC in the "Target Variable:" box which
will be the name of our new variable. Then, type our constant (C) of 6 in the
"Numeric Expression:" box, followed by a space, then a minus sign, then a space.
Next, highlight and move q4 from the available variables box to the "Numeric
Expression:" box using the arrow. Now click on "OK" or "Paste" if you would
prefer a syntax record be created (from which you can highlight and submit the
syntax to perform the compute/recode).
That concludes using the Compute function to recode an item.
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