How do reliability and validity differ? How do they complement each other? Can a measure be reliable but invalid? How?

Question

Quizplus · Accepted Answer

The Answer is Reliability means dependability or consistency.It suggests that the same thing is repeated or recurs under the identical or very similar conditions.The opposite of reliability is a measurement that yields erratic,unstable,or inconsistent results.
Validity suggests truthfulness and refers to the match between a construct,or the way a researcher conceptualizes the idea in a conceptual definition,and a measure.It refers to how well an idea about reality “fits”with actual reality.
Reliability is necessary for validity and is easier to achieve than validity.Although reliability is necessary in order to have a valid measure of a concept,it does not guarantee that a measure will be valid.It is not a sufficient condition for validity.A measure can produce the same result over and over (i.e.,it has reliability),but what it measures may not match the definition of the construct (i.e.,validity).
A measure can be reliable but invalid.For example,you can get on a scale and get weighed.The weight registered by the scale is the same each time you get on and off.But then you go to another scale-an “official”one that measures True weight-and it says that your weight is twice as great.The first scale yielded reliable (i.e.,dependable and consistent)results,but it did not give a valid measure of your weight.

How Do Reliability and Validity Differ? How Do They Complement