Spearman brown coefficient when is it reliable

It takes the split half correlation as input and converts it to an estimate of the equivalent level of reliability for the full-length test.

While this might sound complex, the actual formula is quite simple. As you can see, the formula takes the split half reliability r half as input and produces the full-length estimation r full. This can then be interpreted alongside the ubiquitously used coefficient alpha. Any decent software for classical item analysis will produce it for you. As an example, here is the output of the Reliability Analysis table from our Iteman software for automated reporting and assessment intelligence with CTT.

This lists the various split-half estimates alongside the coefficient alpha and its associated SEM for the total score as well as the domains, so you can evaluate if there are domains that are producing unusually unreliable scores. You can see that, as mentioned earlier, there are 3 ways to do the split in the first place, and Iteman reports all three.

It then reports the Spearman-Brown formula for each. These generally align with the results of the alpha estimates, which overall provide a cohesive picture about the structure of the exam and its reliability of scores. As you might expect, domains with more items are slightly more reliable, but not super reliable since they are all less than 20 items. So, what does this mean in the big scheme of things? Using the same example, we illustrate the principle of "Cronbach's alpha if item deleted" to decide on the poorest performing raters in a set of raters.

The example also emphasizes the need for more raters in the design of the reliability study to obtain a robust estimation of reliability.

Keywords: Classical test theory; Cronbach's alpha; Intraclass correlation coefficient; Reliability; Spearman—Brown prophecy formula. Abstract Objectives: There are similarities between the different forms of reliability, such as internal consistency internal reliability and interrater and intrarater reliability. This entry demonstrates two ways to calculate the S-B formula and show how the predictions in score reliability typically vary with increases or decreases in the numbers of items on a test.

The S-B formula is commonly used to estimate the full-test reliability from the half-test correlation when calculating split-half reliability. Split-half reliability is an internal-consistency strategy for estimating reliability that is similar to the Show page numbers Download PDF. Search form icon-arrow-top icon-arrow-top. Page Site Advanced 7 of