This post will give you some advice about using SPSS to summarise data that were generated with a Likert scale. If you want to read up on Likert scales before you go on, you can find some information in this post.
Why summarise Likert scale data
Elsewhere in this blog, I have written that a Likert scale might consist of several overlapping items. For instance, if I want to measure people’s attitudes towards sweets, I might ask them to record what they think about the following statements:
|1. I like chocolate||Strongly Agree||Agree||Disagree||Strongly Disagree|
|2. I like cookies||Strongly Agree||Agree||Disagree||Strongly Disagree|
|3. Ι Iike whipped cream||Strongly Agree||Agree||Disagree||Strongly Disagree|
In order to interpret these data, we need to summarise the data in the scale. We can do this in two ways: adding the data or estimating the median. In this post, I will show you how to estimate the median, because this is slightly harder. The same steps can be modified to add up the data.
Using the same example as above, I need to create a new ‘super-variable’, which shows the mean of items (1), (2) and (3) for each respondent.
I assume that you will already know how to define variables and values, how to toggle between the numerical expression and verbal descriptor of the values (i.e., you can make SPSS show responses as “strongly agree/agree/disagree/strongly disagree” or as “1/2/3/4”), and how to key in data. I will also assume that you have already established that your scale is internally consistent, so I will focus only on the technical aspects of merging the variables.
Your starting point for summarising Likert scale data with SPSS will be a dataset similar to the one shown in Figure 1, below.
When you have created the dataset by typing your data into SPSS, and after you have tested for the internal consistency of the scale (use Cronbach’s α), it’s time to create a new variable.
Merging the variables
From the top menu bar in SPSS, select Transform -> Compute variable. You should now see the following dialogue box.
- Assign a name to the new variable (e.g., Sweets);
- Scroll down the Function Group, and select Statistical;
- From the functions that appear select the Median. [ΝΒ it is possible to select the mean, but I don’t recommend it]. At this point, the following formula should appear in the numerical expression box: Median ( , )
- Place the cursor in the brackets, select the variables you want to merge, and click on the arrow. Repeat with all the variables, separating them with comas.
- Click on OK.
Your new Likert scale
SPSS will automatically generate a new variable, which will appear at the end of your dataset. This will be in numerical form (1, 2, 3, …), but you can change it to a verbal descriptor for consistency (Figure 3). You can use this variable for descriptive statistics (e.g., estimate the central tendency and dispersion), cross-tabulations, correlations and so on…
Now wasn’t that very easy?
More to read
I hope that this information was helpful, but if there’s anything that was not clear, feel free to drop a line in the comments below. You may also want to check out some more posts I have written on quantitative research, including:
- On Likert scales, levels of measurement and nuanced understandings
- Designing better questionnaires: Using scales
- Four things you probably didn’t know about Likert scales
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