How Z score is calculated for University selection in Sri Lanka

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All subjects are not equivalent. There are easy subjects as well as difficult subjects. There are high scoring subjects and low scoring subjects. Marking also can vary: there can be strict marking or liberal marking in different subjects. As such, aggregate of different subjects is not a fair criterion to give an overall rank to a student. Therefore use of simple average (aggregate) Marks is not a good method to determine eligibility for university admission.

For example, marks of one subject could have a range from 5 to 70 while the range for another subject spans from 45 to 99. A student who obtained 70 is the best among the lot in the first case and the one who obtained 70 in the second case is a mediocre student. When the simple aggregate is taken for admission, the best student in the first case is treated equally to a mediocre student who opted for a relatively easy subject as in the second case.

This issue was the theme for a series of discussions in academic circles and in spite of several advanced methodologies available for standardisation, Z score approach was adopted about ten years back as the criterion for university admission due to its simplicity, computational convenience, application efficiency and the need for only two parametric estimates for its calculation.

What is the Z-score and how it is calculated?

The Z-score is calculated by subtracting the raw mark of the subject by the mean mark of the subject, and then dividing by the standard deviation of the marks of the subject. (see graphic).
Z-Score formula
Z score what is z score in sri lanka
The Z-score for a given subject is comparable to the Z-score of another subject, although raw marks are cannot be compared.

In the Z Score method the average of each subject is brought to 0 and the spread is usually from +3 through 0 to -3. Z Score gives the candidates the position in each subject with respect to the average mark scored by the candidates in that subject. Z Score therefore ranges from around +3 to -3 (e.g. +1.252, +2.012, -o.958 etc.). Then, the average Z Scores of the 3 or 4 subjects of the candidates are taken as the final Z Score, which will be used to rank the students in each stream, island-wide and district-wise.

Citing an example, Prof. Thattil said the raw mark of 50 for Physics may be an above-average mark, while for Geography it may even be below the average.

Although mean and variance of raw marks can differ from subject to subject, the Z-scores are distributed with a mean of zero and variance of 1, for any subject – effectively bringing all subjects to a common ground. Simply put, the marks of the subjects are thus standardised to make way for fair university admissions.

Eg- Comparison of Z Scores of Two students

Z score 3 subjects

Z score 3 subjects

Z Score different subject combinations

Z Score different subject combinations

District quota system in University Admission

District quota system According to the present university admission policy, the admission to each course of study (e.g. Medicine, Engineering, Agriculture, etc.) is governed by the following quota system, except in the case of Arts where the admission is made on all island merit basis.

All island merit basis 40%

District basis 55%

Additional quota or educational Disadvantage districts 05%

This district quota will be allocated to the 25 administrative districts on the ratio of population of the district concerned to the total population in the country in respect of each course of study. Similarly, the 5% quota for the underprivileged districts will also be allocated in proportion to the population of each such district. There are 13 districts which have been declared as educationally disadvantaged districts by the University Grants Commission.

These districts are: Nuwara-eliya, Hambantota, Jaffna, Kilinochchi, Mannar, Mullaitivu, Vavuniya, Trincomalee, Ampara, Anuradhapura, Plonnaruwa, Badulla and Moneragala.

Available places in each course of study in the University system will be filled according to this national policy. This will be done by ranking candidates using their final Z Scores. After processing the university admission applications, the UGC will determine and announce the cut off Z Scores for each course of study in respect of each district, as practiced earlier.

Z-Score values for Previous years for various subjects

Z scores for University courses 2011- 2012 academic year (2011 A/L examination)

Z scores for University courses 2010- 2011 academic year (2010 A/L examination) –

Varsity hopefuls from 2012 A/L batch face uncertain future

Z Score and Advanced Level results: The intricate story

Ranking candidates on Z Score instead of aggregate by Professor R. P. Gunawardane



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