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A one-tailed test should be used only in a study in which an effect in the unexpected direction is functionally equivalent to no effect. It is not appropriate to use a one-tailed test simply because one is able to specify the expected direction of the effect prior to running the study. In medicine, for example, we typically expect that the new procedure will improve the cure rate, but a finding that it decreases the cure rate would still be important, since it would demonstrate a possible flaw in the underlying theory. For a given effect size, sample size, and alpha, a one-tailed test is more powerful than a two-tailed test (a one-tailed test with alpha set at .05 has approximately the same power as a two-tailed test with alpha set at .10). However, the number of tails should be set based on the substantive issue (will an effect in the reverse direction be meaningful).

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Q: When is it valid to use a one-tailed test?
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Related questions

A test may be reliable but not necessarily validIs it possible for a test to be valid but not reliable?

No, for a test to be valid, it must also be reliable. Reliability refers to the consistency of the test results, while validity refers to the accuracy of the test in measuring what it is supposed to measure. A test cannot be valid if it is not reliable.


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In my view reliable test is always valid.


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Yes, it would be a valid test.


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Yes sure. It is valid. It will shows the how fast you are thinking.


Why is it possible to have a reliable measure that is not valid but impossible to have a valid measure that is not reliable?

A reliable measure is consistent and yields consistent results, so it may not be measuring the intended construct accurately (lack validity). On the other hand, a valid measure accurately assesses the intended construct, but it must be consistent and produce stable results (reliable) to ensure that the measurements are dependable and trustworthy.


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You will have to try it out. Go to the Lowes website and test it out. If you punch the code in and it is accepted then you will be able to use it.


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