Did you notice the new Cronbach’s Alpha with Delete column under the symbol ɑ- in GradeHub’s item analysis? So what is ɑ -?
Cronbach’s alpha with delete removes the question you’re reviewing and recalculates the exam’s overall reliability (i.e., Cronbach’s Alpha, sometimes called, Correlation Alpha or Alpha for short) calculation without it. Here’s an exceptional blog post on Cronbach’s Alpha by Dr. Charles Zaiontz.
Along with the point-biserial correlation and upper and lower 27% analysis, “Cronbach’s alpha with delete” will help you understand the quality of a given test question. As you would expect, these three measures provide similar insights and are highly correlated. You can create better exams by reviewing these measures of item quality. In some cases, a negative point biserial or Cronbach’s alpha with delete might cause you to remove a question from the exam before finalizing grades. You can do that easily in GradeHub by changing the questions point value to zero.
In GradeHub, if the Cronbach’s alpha with delete text is red, that means the reliability of the exam goes up if you remove the question from the test. In other words, the exam is better off without the item. Conversely, a “good” question will have a Cronbach’s alpha with delete lower than the exam’s overall reliability. The differences between Cronbach’s alpha with delete and the exam’s Cronbach’s alpha will likely be small due to the number of test questions.
Happy grading,
Mark