Psychometric Test Reliability

When choosing a reputable test, whether it be an aptitude test or a personality test, one of the properties of the test you will need to look for is reliability. We’ll consider reliability in appropriate detail in a later section of the course. For now, think of reliability as consistency. In order to have absolute confidence in our test scores we need them to be consistent. However, we can’t test and retest our candidates in the real world. Despite this, reputable test publishers would already have done this for you. This would have been carried out under optimal conditions. So, now you know that you are using a reliable test (one that produces consistent scores), it’s your task as the test administrator to ensure that the test remains a reliable test.

Why is reliability so important for psychometric test administrators?

Whenever you assess something, you expect the score you get to be reliable. For example, if you assess your weight using bathroom scales, you expect the reading you get to be consistent across at least the short term. If you weigh yourself over 2 consecutive days and get significantly different readings you know something is wrong with the scales! The same is true of psychometric tests. The reputable test publisher first ensures that the test scores will be consistent over time and then you, as the administrator, need to ensure that your actions do not make the test less reliable.

Not only do we want and expect test results to remain reliable over time, but we also know that reliability is a precursor to validity. It sets an upper limit on the test’s validity. In other words, if your test is not reliable then it is not valid. Confusing? Let’s use the weighing scales example again…

Let’s suppose a medical doctor does some research which shows that those who weight more than 120kg are significantly more likely to suffer a heart attack. His research shows that weight is a valid indicator for predicting the heart attack. The scales are fit for the purpose of predicting a heart attack. Validity is all about being fit for purpose. Now if those scales are not reliable, they will provide inconsistent data over the time of the research program. In this case would you have confidence in the doctor’s findings? Of course not!

So, to apply this to psychometric tests let’s take an aptitude test. We’ve carried out research which confirms that a new numerical reasoning test can predict the performance of accountants. Those who score better on the test are rated as better accountants. This is validity. The test is fit for the purpose of predicting accountant performance. You will hopefully have full confidence in this finding if you know the test is reliable. If however you expect the test is coming up with inconsistent scores for your candidates, it is unreliable, and, as in the scales example above, you will not have confidence in the test’s prediction of accountant performance. This is why reliability is a precursor to validity.

And why is all of this so important for this course? It’s because you as the test administrator can enhance or reduce the reliability of the test by how you administer it in the first place.

We’re pleased to provide complimentary temporary access to the section of our online training in psychometrics that explains the above points. Simply click the image above to continue.