Often times in quantitative research, we can confuse reliability and validity since they can be quite interwoven in their implications toward each other. From Creswell (2012), I have found the following delineations:
Reliability – scores or indicators need to be consistent and found similar when they are testing the same things (p. 159).
Validity – is the evidence that the test is measuring what it is supposed to measure (p. 159).
In the big picture, we need to have consistent scores (i.e. reliability) that assist with evidence that we are measuring what we intend to measure (i.e. validity).