Validity and Reliability

Post date: Aug 26, 2012 4:45:48 PM

Two views about the relationship between validity and reliability.

1. Some people argue that reliability is a necessary but not sufficient component of validity. That is, if a measurement is valid, then it is also reliable. But just because it is reliable doesn't mean it is valid. A baseball player may reliably strike out, but he's still not a good batter. A butcher who weighs your meat with his thumb pressed down on the scale may be quite reliable, but his figures always come out too high.

2. Others argue that the concepts are orthogonal to each other, as in the following table.

The graphic below portrays the same idea.