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Re: facility and discrimination

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Date:

Fri, 23 Mar 2001 09:27:33 +0000

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 ```Here's the address of the documentation for staff here at Leeds on using MCQ papers in our VLE. http://www.leeds.ac.uk/sociology/nbmanual/nbb4v2.pdf Section 9 deals with the statistical analysis of class results. Correlation is used on questions that give a sliding scale of performance, e.g. multiple response questions and AnoVa is used where it is a right/wrong score. For the former marks on a questions are correlated against marks on the exam as a whole or against some other performance indicator provided to the software. The correlation coefficient can be interpreted in a similar way as a discrimination index - it is a number between -1 and +1. A value of +1 indicates a perfect linear relationship between performance on the question and performance on the "reliable" measure of performance, -1 also indicates a perfect linear relationship but in reverse. A score of 0 indicates that there is no relationship between performance on the question and performance on the test as a whole. The correlation is accompanied by a probability that the coefficient deviates from 0 due only to random variation in the data. The statistic from AnoVa is the difference in performance for two groups of students - those who got this question wrong and those who got it right. This is expressed as the gap in the student's mean mark on some reliable performance indicator. Like a discrimination index a positive value shows that the students who got this question right were the generally more able students and a negative value shows that they were the generally less able students. If you want to program these stats into your tools the maths can be found in any reasonable stats text book. If you are willing to do it "by hand" you can use the analysis toolpack standard add-in for MS Excel. Jon Carole McLennay wrote: > > Many thanks to all who kindly provide such helpful advice. I can see how > useful the significance level would be and I, too, would be grateful for > details of both the AnoVa and the correlation usage > > Carole. > > > > My personal preference is to use AnoVa or correlation (depending on the > > scoring scheme for the question) to analyse class performance. A > > correlation coefficient has the same usefulness as for example a > > disrimination index but it is accompanied by a significance level so > > you know when to take it with a pinch of salt. > > > > I can give some details of this if people think it will be of interest > > and I would welcome criticism. > > > > Jon Maber > > > > ```