Confidence intervals in psychological tests

[DrDu]

Recently I saw the results of an IQ test given with confidence intervals. While I know very well what a confidence interval is, I am not sure how you can give one for a psychological test. I think to determine a CI you either have to know the "true IQ" of an ensemble of persons and see how the results of the test scatter. Or you must be able to repeat the test with the same person and see how the results scatter on repetition. However, you neither know the true IQ nor can you repeat the same test with the same person as it will remember previous results.

 

[Monstrous Math]

IQ is an ambiguous term, so it seems doubtful that there is a "true" IQ that is always the same for that person. If the person is very very tired, for example, it can skew the results. Or if the person is on a drug. Or in love. Or whatever. In any case, even if you did know the true IQ, you wouldn't need a confidence interval. Confidence intervals are used because one is uncertain. As for what specific data they used for their confidence interval, you'll have to get that from the researcher. It's hard to discuss data we're in the dark about.

 

[DrDu]

I know that the IQ can vary. My question is not specific to the IQ but how you define confidence intervals in general for psychologic quantifiers where you have problems with repeatability for one subject.

 

[256bits]

The confidence interval would refer to the sample population and NOT the individual. The test score is what the individual received with a margin of error

It describe the score one receives on his/her IQ test of being part a sample and how reflective it is to the whole population.

In other words it is comparing a sample population, of which the testee is part of, to the whole population, and then asking if the testee then does belong to a sample, of all the samples that can be taken of the population, reflecting the parameters of the population, or not.

 

[LudusRex]

I can understand your confusion about confidence intervals in psychological tests. While confidence intervals are commonly used in statistical analysis to estimate the precision of a measurement, it can be challenging to apply this concept to psychological tests.

In psychological testing, the concept of "true IQ" is not as straightforward as it may seem. IQ is a complex construct that is influenced by various factors such as genetics, environment, and individual experiences. It is not a fixed value that can be measured accurately, making it difficult to establish a "true IQ" for a group of individuals.

Additionally, as you mentioned, repeating the same test with the same person may not provide accurate results as the individual may remember their previous responses, leading to bias in the data. This is known as the practice effect, and it is a common issue in psychological testing.

Therefore, when determining confidence intervals in psychological tests, researchers often use other statistical methods such as standard error of measurement or test-retest reliability to estimate the precision of the results. These methods take into account the inherent variability and limitations of psychological tests.

In conclusion, while it may be challenging to apply the concept of confidence intervals to psychological tests, researchers use alternative methods to estimate the precision of the results. It is essential to consider the unique nature of psychological testing when interpreting and evaluating the validity of these tests.