SB defends Z score formula; Parliament takes up A/L results mess-up:
Higher Education Minister S. B. Dissanayake yesterday told Parliament that the Z-score formula was only a mathematical formula and not an invention by Prof R. O. Thattil.
In reply to a statement by Opposition Leader Ranil Wickremesinghe that the creator of the Z- score formula Prof Thattil, too, was against the way the formula had been distorted by the Department of Examinations causing a mess-up in the GCE (A-Level) results, Minister Dissanayake said the fact that the examination would be conducted under two syllabuses had been known to all stakeholders for the past three years or so.
There was a need for obtaining the mean value of the marks obtained by every candidate to select him or her for university admission, he said.
Minister Dissanayake said: “Prof. Thattil faults us for not including him on the expert panel to look into the problem. He was not invited to the committee because he had submitted a document in a court case a few years back that the Z score was incorrect and the court had rejected it. That was why we did not invite him this time around.”
The Z score formula was introduced in 2000 to scale the GCE (A-Level) results so that the average of the Z scores received for different subjects could be used in ranking, Minister Dissanayake said.
Courtesy: The Island
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As far as Z score calculation is concerned decimal points cannot be ignored. 0.5 differences in mean values and standard deviations makes it impossible to pool them using a combined mean due to the fact that Island ranks are based on z scores, and a difference in a decimal points in Z score could have large errors on Island ranks. Differences in Island ranks can be 500 or 1000 ranks below similar results in two examinations. Depending on the raw marks in different subjects and depending on differences in mean values in different subjects irregular z scores can be received by candidates. It is a real mess up in a disorderly manner students from both examinations can be affected in a disorderly manner.
Different persons give different ideas on this contravosial topic who dont have enough knowledge of educational measurements.Other thing is anyone cannot say more accurate method to use in such a situation.In a case of 2 populations and 2 exam papers we have to calculate Z scores seperately,it is easy and accurate,but if we need to put them in a single scale we should thoroughly study the behaviour of both marks and interpret then in order to combine the Z values.In large populations some errors may be occured.But errors can be minimized with experts.No one can propose any formular to combine both ranks without studing the behaviour of the both groups of marks.No one cannot combine these Z scores without errors.If students are selected 50 to 50 or any other ratio of 2 ranks other can argue.
These talkings are based on different peoples personals agenda.Anyone can easily blame to Examination Department.But it has a proud and clean history.Dogs can bark to a mountain,but it will not shake.
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