In this "quick start" guide, we will enter some data and then perform a transformation of the data. Transforming data is performed for a whole host of different reasons, but one of the most common is to apply a transformation to data that is not normally distributed so that the new, transformed data is normally distributed. Transforming a non-normal distribution into a normal distribution is performed in a number of different ways depending on the original distribution of data, but a common technique is to take the log of the data. In this example, we will show you how SPSS Statistics allows you to do this.
In practice, there are infinite possible ways to tranform data, although there are some approaches that are much more common than others. In our enhanced content, we show you how to transform your data using SPSS Statistics for "square", "square root", "reflect and square root", "reflect and log", "reciprical", "reflect and inverse" and "log" transformations. We also explain how to transform data that ranges from being moderately to extremely positively or negatively skewed. You can learn more about our enhanced content here.
In the six steps that follow, a transformation using SPSS Statistics is performed on the following example data:
Data to Transform | |||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
36 | 32 | 45 | 41 | 29 | 22 | 18 | 36 | 10 | 40 | ||||||
Table:Data to enter into SPSS Statistics. |
Your data should end up looking like the following:
Note: Remember that each individual's results go on a separate line (row) in SPSS Statistics.
Published with written permission from SPSS Statistics, IBM Corporation.
Rename the variable, "Data", instead of the default, "VAR00001".
Note: You can name it something else if you wish. We have just called the variable "Data" for our example.
Click on Transform > Compute Variable... in the top menu, as shown below:
Published with written permission from SPSS Statistics, IBM Corporation.
You need to first select the function you would like to use. To do this, click "All" in the Function group: box, then scroll down in the Functions and Special Variables: box and click "Lg10" to select it.
Transfer the Lg10 function into the Numeric Expression: box by pressing the button.
Click the Data variable in the left-hand box and then click the button, which will result in the expression you see in the Numeric Expression: box below.
All you need to do now is give this new variable a name. We have called the new variable TrData. Type this name into the Target Variable: box in the top left-hand corner.
Published with written permission from SPSS Statistics, IBM Corporation.
Click the button.
You will be presented with the SPSS Statistics Data Editor, which will now show the log transformed data under the new variable name "TrData" that you defined, as shown below:
Published with written permission from SPSS Statistics, IBM Corporation.