A T Score (sometimes hyphenated T-Score) is a common example of a scaled score in psychometrics and assessment. A scaled score is simply a way to present scores in a more meaningful and easier-to-digest context, with the benefit of hiding the sometimes obtuse technicalities of psychometrics. Therefore, a T Score is a standardized way that scores are presented to make them easier to understand.
What is a T Score?
A T score is a conversion of the standard normal distribution, aka Bell Curve. The normal distribution places observations (of anything, not just test scores) on a scale that has a mean of 0.00 and a standard deviation of 1.00. The T Score simply converts this to have a mean of 50 and standard deviation of 10. This has two immediate benefits to most consumers:
- There are no negative scores; people generally do not like to receive a negative score!
- Scores are round numbers that generally range from 0 to 100, depending on whether 3, 4, or 5 standard deviations is the bound (usually 20 to 80); this somewhat fits with what most people expect from their school days, even though the numbers are entirely different.
The image below shows the normal distribution, labeled with the T Score and also Percentile Rank for interpretation.
How to interpret a T score?
As you can see above, a T Score of 40 means that you are approximately the 16th percentile. A 70 means that you are approximately the 98th percentile – so that it is actually quite high though students who are used to receiving 90s will feel like it is low!
Since there is a 1-to-1 mapping of T Score to the other rows, you can see that it does not actually provide any new information. It is simply a conversion to round, positive numbers, that is easier to digest.
Is a T Score like a t-test?
No. Couldn’t be more unrelated. Nothing like the t-test.
How do I implement with an assessment?
If you are using off-the-shelf psychological assessments, they will likely produce a T Score for you in the results. If you want to utilize it for your own assessments, you need a world-class assessment platform like FastTest that has strong functionality for scoring methods and scaled scoring. An example of this is below.
Nathan Thompson, PhD
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