Psychometrics: Test Reliability and Validity?

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Please see the response attached, which is also presented below.

Explain each of the following in your own words. If appropriate, give an example.

a) Difference between reliability and validity of a test.

Reliability is the consistency of your measurement, or the degree to which an instrument measures the same way each time it is used under the same condition with the same subjects. A measure is considered reliable if a person's score on the same test given twice is similar. It is important to remember that reliability is not measured; it is estimated. (1)

The real difference between reliability and validity is mostly a matter of definition. Reliability estimates the consistency of your measurement, or more simply the degree to which an instrument measures the same way each time it is used in under the same conditions with the same subjects. Validity, on the other hand, involves the degree to which you are measuring what you are supposed to. For example, if you measure self-esteem with a depression scale, the scores are not an accurate measure of the level of your self-esteem. We would conclude that the depression lacks validity, when used to measure your self-esteem. Thus, validity is a measure of accuracy. However, it is still considered reliable, because your scores were consistent on the depression test given to you twice. (1)

Does this make sense?

b) Can a test be reliable but not valid? Explain through an example.

A test can be reliable but not valid. Reliability is about consistency of scores. So referring to our example above, let's say that the ...