What does it mean to say that a test can be no more valid than it is reliable?

Hi, My specializtion in Psychology is IO so I thought that I would
have a crack at this question.

Firstly I think that it is important to distinguish between validity
and reliability.

Reliablity basically means that a test or experiment can be
administered over and over again and you will reliably be able to
measure something. For example you may have adminstered a test to five
patients that have a condition and the test will show that they have
the condition, it does not mean that the test actually worked just
that it was reliable.

In general Validity refers to weather the test actually meaures what
it claims to measure. So for example we took 10 patients, and we know
that five have a condition and five do not, then does the test when
administered blindly does the test pick the five that have the
condition and the five that do not have the condition.

One of the ways that I think about it is to restate it in another way.

A test can be reliable without being valid, but you cannot have a test
that is valid without being reliable.

Let me know if this answers your question.

Here's another example to build from jba2905...

Reliability is similar to consistency and validity is similar to
accuracy.  I like the dart board example.  If you throw darts
reliably, they will always land in the same area...it might not be at
the bulls-eye, but it will be in the same place.  Validity is actually
hitting the bulls-eye.  So even if you can hit the bulls-eye
(validity), if you can't do it consistently (reliability) there's not
much point.

So bottom line...even if you come up with a test to measure something
accurately (validity), if you can't measure it consistently
(reliability) the test won't do much for you.

to: jba22905 and needsomeinfo:  These are very explanatory. I have a
difficult time explaining what I know in writing even though it's in
my head.  Thesea re great.  Thanks much.

Did it answer your question

Personally, I think graduate-ga has indeed said his question is
answered. Good Job!!!

~~Cynthia