![]() The image below is example output from Iteman, where Rpbis is the point-biserial. This is an important step in item analysis. Of course, psychometric software like Iteman will also do it for you, and many more important things besides (e.g., the point-biserial for each of the incorrect options!). Since it is a Pearson correlation, you can easily calculate it with the CORREL function in Excel or similar software. If you calculated a correlation, it would be around 0.10. If you fit a regression line, it would have a positive slope. The scores are definitely higher for the Correct group. There are 10 examinees that got the item wrong, and 10 that got it correct. As such, it is sometimes called an item-total correlation.Ĭonsider the example below. The point-biserial coefficient is a Pearson correlation between scores on the item (usually 0=wrong and 1=correct) and the total score on the test. ![]() This is a total red flag it means that good students are getting the item wrong and poor students are getting it right, which almost always means that there is incorrect content or the item is miskeyed. If the reverse is the case, then the discrimination will be negative. If this isn’t the case, and the item is essentially producing random data, then it has no discrimination. If a math item on Fractions is good, then students with good knowledge of fractions will tend to get it correct, while students with poor knowledge will get it wrong. It means that it is differentiating between examinees, which is entirely the reason that an assessment item exists. While the word “discrimination” has a negative connotation, it is actually a really good thing for an item to have. Item discrimination is a psychometric concept regarding the quality of a test item, and the point-biserial coefficient is one of several indices for this concept. Lecture Notes – Online Course in Psychometrics and Assessment.TestAssembler (Automated Form Assembly).FastTest – Item Banking & Online Testing.Ranges from -1.0 to +1.0 the closer to 0. Computed by subtracting the number of successes by the low group on the item from the number of successes by the high group, and divide this difference by the size of the class. If the intent is a discriminating question, a range of 0.30 to 0.70 is generally acceptable.ĭiscrimination index – This value is based on the top 27% and bottom 27% of the class on the exam. If the intent is a mastery item, a difficulty level between 0.80 and 1.00 is acceptable. There is no a set number the item difficulty must be taken into account with the point Biserial and discrimination index. Item Difficulty – Acceptable item difficulty is how many exam takers answered the item correct. General guidelines for ExamSoft statistical interpretation are as follows: In general a KR-20 >0.50 is acceptable with at least 30 exam takers, 50 items, and only one correct answer for each item. KR-20 may not be useful if exams are not reused every year.The fewer number of questions, fewer number examinees, and multiple key adjustments will almost always lead to a misleading and low KR-20 value.Number of students taking the assessment.Number of questions on the assessment (>50 is ideal).Value is influenced by several factors.KR-20 ranges from 0.0 to 1.0 the closer to 0 indicates a very poor reliability and closer to 1.0 indicates high reliability.Used as an overall measure of reliability for an assessment.The figure below shows an example of an item analysis report from ExamSoft (Note: Question stem and answers redacted): Data elicited from this type of analysis contains information essential for identifying strengths and weakness of the instrument. Statistical analysis of test item data is useful for faculty to achieve valid and reliable assessment instruments in order to appropriately measure student performance. Office of Equity, Diversity and Inclusion.Banner - University Medical Center Phoenix.Translational Cardiovascular Research Center.Center for Toxicology and Pharmacology Education and Research.Center for Applied NanoBioscience & Medicine.Aerospace Medicine and Surgery Fellowship.Family, Community and Preventive Medicine.Molecular and Cellular Neurogenetics Laboratory.Health Humanities Certificate of Distinction.Banner – University Medical Group Faculty.Campus Parking & Transportation Services.Biomedical Sciences Partnership Building.Tips for Transitioning to Medical School.
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