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Tuesday, October 23, 2012

PSLE T-Score: The Role of the Mean

This post is the second of a pair of posts relating to the PSLE T- Score. The first describes the role of the Standard Deviation in the PSLE T-Score and can be found HERE. The PSLE T-Score formula is as follows...

You will notice that both the Mean and the Standard Deviation is necessary in the calculation of the PSLE T-Score. This post therefore, examines the role of the Mean in the determination of the PSLE t-score.

The mean is the average score of the entire cohort. It is a measure of paper difficulty. If the average score is low, the paper is difficult. If the average score is high, the paper is easy. How then does the difficulty of the paper affect the contribution to t-score? Let us pretend the 20XX's 4 subjects were difficult as follows...

(1) Math - Difficult (low cohort average)
(2) Chinese - Kinda Difficult (kinda low cohort average)
(3) English - Ok (not too low and not too high cohort average)
(4) Science - Easy Peasy (high cohort average)

In the table below I have fitted the PSLE T-score formula to a student who scores 100 marks for all 4 subjects. You can see that the higher the difficulty of the paper (i.e., the lower the cohort average), the higher the contribution to t-score.

For those whose next questions are...
(1) How do we compute the cohort averages and cohort standard deviations?
(2) Does the Ministry of Education release these numbers?

Parents can't calculate cohort averages and cohort standard deviations. You need to know the marks of all the students who took the exam to calculate these. The MOE also does not announce these numbers.

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