People are frequently asked to rate something on a scale of 1 to 10. Let’s take the pain Numeric Rating Scale (NRS-11) as an example. 1 means low pain (bump), 10 means extreme pain (migraine). Now what would warrant a 2 or a 9? A person simply can’t categorize pain into 10 different levels. The NRS-11 groups the 10 pain levels into 3 categories (Mild, Moderate, Severe). Why not just use a 3-point scale or the category names?
I postulate that most 10-point scales can be replaced with 5-point scales with no loss of information. For analysis purposes, most responses are going to be grouped into 3 – 5 categories or averaged.
Conversion of existing 10-point data values to 5-point data values is easy.
- Add 1 to the 10-point value
- Divide the result by 2
- Drop the fractional part
Example for value 9:
- 9 + 1 = 10
- 10 / 2 = 5
Example for value 10:
- 10 + 1 = 11
- 11 / 2 = 5.5
- Drop the .5 = 5