PERSPECTIVE Education Plus

# Percentile-based ranking process

Photo: R. V. Moorthy

The hustle and bustle in MBBS admissions this year against government quota seats in Tamil Nadu has brought to fore possible anomalies in the procedure currently followed for admission. The wide variation in the number of centums obtained in Physics (P), Chemistry (C) and Biology(B) in the current year and the last year, attributed to varying ‘toughness’ of the question papers and evaluation, is undoubtedly the culprit and its influence must definitely be eliminated.

A percentile-based ranking may be adopted to get over this problem.

What is percentile?

Consider a list of marks of a certain set of students in some subject arranged in descending order (that is, the rank list, based on marks). The percentile obtained by a student in the list is the ratio of the number of students who have obtained marks less than his marks, to the total number of students, converted to a base total of 100 students. In other words, it is the percentage of students above whom he stands in the mark-based rank list.

Thus, if N is the total number of students and if this student’s position in the rank list is q, then his percentile is p = 100 (N - q) / N. (It can be easily seen that p is 0 for the last student, nearly 100 for the first student and around 50 for the one who is in the middle of the table. Also, the first and the third quartiles are the percentile values corresponding to q = 3N/4 and N/4, respectively). This measure thus compares the student’s merit with that of others of his own class and is not affected by the magnitude of the maximum/minimum marks in the list, which is a crucial advantage of this measure.

Every year the Secretary, Admission Committee for MBBS, (or any other competent authority vested with this responsibility), shall procure from the Director of Government Exams, the marks in +2 in the subjects of P, C and B obtained by all candidates who have passed +2 in that year in the Tamil Nadu scheme. The subsequent steps can be as follows:

For all these students, what we can call as ‘Rank Marks’ (which are mistakenly called as ‘cut-off mark’ by certain others) shall be prepared as being done now, (computing the marks in P, C and B for 50, 50 and 100 respectively and adding, for a total of 200), and the rank list based on these rank marks be prepared. (Any ‘ties’ arising need not be ‘broken’ now.)

The percentiles for all candidates in this list must be calculated and a ‘Percentile Rank List’ prepared. (Again, any ties in this list need not be resolved now). Identify and retain in the list only those who have applied for admission this year. We now have the Percentile List of applicants for MBBS admission under the Tamil Nadu government quota, who have passed +2 this year under State Board scheme.

Similarly, prepare the Percentile List of applicants for MBBS admission under the Tamil Nadu government quota, from those who have passed +2 this year under the CBSE scheme. Similar other schemes must also be likewise considered. No normalisation need be done. The process takes care of it.

By merging together all these percentile rank lists obtained in steps 2 and 3 above, a consolidated percentile rank list of all candidates for admission, who have passed +2 this year in different schemes, is obtained.

Such consolidated lists must be prepared for those few previous years also if you find applicants in the current year having passed +2 in those years.

Merge all the above consolidated rank lists (as obtained in steps 4 and 5) into one. Now break ties, if any, using appropriate norms (which may be the ones used now). What you now have is the final totally acceptable rank list based on which counselling and admission can be done without any grudge from any quarters — on variations in the number of highest marks in different years, differences in schemes of education, methods of evaluation, relative ease/toughness of question papers and the like.

Though the above scheme is detailed only with reference to admission to MBBS, the same is applicable to any other programme as well, with suitable modifications. There will also be no need for any separate normalisation.

The widely accepted other global level admission procedures like SAT, GRE and GMAT, use percentile-based ranking, only because of its advantages mentioned above. For some of these tests, the scores are valid for as many as five years, and still no grudges are voiced against their procedures only because of the soundness of the scheme adopted.

It can be further noted that these are only common tests conducted for special purposes, but still percentiles are preferred over raw marks for ranking. On the other hand, in our case, there are more disturbing parameters, mostly due to lack of common entrance examinations, and dependence only on the qualifying exam marks, more than one scheme of qualifying study, variations in ‘toughness’ of question papers and evaluation procedure, and so on. All these will necessitate and justify the use of a better and more credible procedure for admission, as the percentile-based ranking process described above.

The writer is former professor and head, entrance examinations and admission, Anna University, Chennai.

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