used to estimate how much a test's reliability will increase when the length of the test is increased by adding parallel items.Step 3: Adjust the half-test reliability using the Spear-man-Brown formula ![]() Step 2: Compute a Pearson r between scores on the two halves of the test. Step 1: Divide the test into equivalent halves. Cronbach's alpha is a less conservative estimate of reliability than test/retest. In the end, your computer output generates one number for Cronbach's alpha - and just like a correlation coefficient, the closer it is to one, the higher the reliability estimate of your instrument. In short, Cronbach's alpha splits all the questions on your instrument every possible way and computes correlation values for them all (we use a computer program for this part). For example, you could write two sets of three questions that measure the same concept (say class participation) and after collecting the responses, run a correlation between those two groups of three questions to determine if your instrument is reliably measuring that concept. ![]() Internal consistency estimates reliability by grouping questions in a questionnaire that measure the same concept. Instructions, time limits, assertation examples formed should be equal. ![]() ![]() The range and level of difficulty of the items should also be equal. The test should contain the same number of items and items should be express in the same form and should cover the same type of content.
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