Importance of Reliability and Validity:
Both reliability and validity are important when critiquing a measure or research study. However, they are two totally different terms with different meanings.
Reliability refers to the extent of which the instrument is consistent when measuring the construct.
Validity on the other hand refers to the extent at which the instrument actually measures the construct that it is supposed to be measuring.
Still confused?
In simpler words, if I was measuring the length of my foot with a tape measure and got 108 inches each time that I measured it, then this would be an example of a reliable measure. This is reliable because each time (8 total times) I measured, I got the same answer; 108 inches. The tape measure is giving me a consistent answer. However, this would not be valid because the actual size of my foot is 84 inches, not 108 inches. The tape measure was not measuring something that it was supposed to be measuring. So in this case, the tape measure would be valid measuring my foot. In essence, it is obvious that a measure can be reliable but not necessarily valid.
Reliability refers to the extent of which the instrument is consistent when measuring the construct.
Validity on the other hand refers to the extent at which the instrument actually measures the construct that it is supposed to be measuring.
Still confused?
In simpler words, if I was measuring the length of my foot with a tape measure and got 108 inches each time that I measured it, then this would be an example of a reliable measure. This is reliable because each time (8 total times) I measured, I got the same answer; 108 inches. The tape measure is giving me a consistent answer. However, this would not be valid because the actual size of my foot is 84 inches, not 108 inches. The tape measure was not measuring something that it was supposed to be measuring. So in this case, the tape measure would be valid measuring my foot. In essence, it is obvious that a measure can be reliable but not necessarily valid.