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What is PBCC?

This article explains the PBCC (Point-Biserial Correlation Coefficient).

On the Item Analysis table of the your IRAT Dashboard, the heading of the last column reads PBCC.

PBCC, also referred to as the Point-Biserial Correlation Coefficient shows the relationship between how the learner performs on the item and their total test score.

  • The range is from –1.00 to 1.00.
  • The higher the value, the more discriminating the item. This indicates that learners who got high test scores got the item correct, whereas learners who had low test scores got the item incorrect.
  • Items with discrimination values near or less than 0 should be removed from the test. This indicates that learners who did poorly overall did better on that item than learners who did well overall. 
  • The acceptable range: 0.20 or higher
  • The ideal value: Closer to 1.00.



where:unnamed__2_.png= The mean total score for persons who have responded correctly to the item 

unnamed__3_.png= The mean total score for all persons

 unnamed__4_.png= The difficulty value for the item 

unnamed__5_.pngp-1unnamed__6_.png= The standard deviation of total test scores 

How does InteDashboard calculate the PBCC of the Point-spreading type of IRAT?

InteDashboard treats partials scores as zero. This means that if a learner in a confidence-based test gets 50% points in the question, we treat it as wrong because they are not 100% correct.