Module 3: Reliability (screen 2 of 4)
Reliability and Validity

As mentioned in Key Concepts, reliability and validity are closely related.  To better understand this relationship, let's step out of the world of testing and onto a bathroom scale.

 

 If the scale is reliable it tells you the same weight every time you  step on it as long as your weight has not actually changed.   However, if the scale is not working properly, this number may not  be your actual weight.  If that is the case, this is an example of a  scale that is reliable, or consistent, but not valid.  For the scale to  be valid and reliable, not only does it need to tell you the same weight every time you step on the scale, but it also has to measure your actual weight.

 

Switching back to testing, the situation is essentially the same.  A test can be reliable, meaning that the test-takers will get the same score no matter when or where they take it, within reason of course.  But that doesn't mean that it is valid or measuring what it is supposed to measure.  A test can be reliable without being valid. However, a test cannot be valid unless it is reliable.