Spoilt for choice

This time of the year, exam is the buzzword.  Every house is plagued by it. If you pick any random human sample, it could be a student victim preparing for an exam; an overstressed parent or a peer pressured sibling(s)/classmate.

“Worry” is the only perceptible truth in the education sector this time of the year.  As a teacher, I am worried as well. My anxiety comes from my recent experience where I was engaged in a discussion with a student about Multiple Choice Questions (MCQ) that had appeared in a competitive exam.

There is an ongoing debate in about using MCQs to evaluate students’ knowledge, understanding and their ability to apply it.  Some are in agreement with MCQs – and some are not. Those who agree see the potential of this for mass evaluation.  Those who don’t see the problems inherent in such a system.

For a teacher like me, the MCQ method of evaluation is highly problematic. Let us consider the following example:

There is an air bubble of Volume Vo at the bottom of a tank containing water.  The height of the tank is h.  The air bubble increases in volume as it rises up to the surface and become 2 Vo when it is just at the surface of the water.  Assuming that temperature of the atmosphere and atmospheric pressure to be constant (=105 N/m2), calculate height of the water tank. Take density of water is 1000 kg/m3 and g = 10 m/s2.

(a)   5 m      (b) 10 m            (c) 20 m            (d) 25 m

A typical student approaches this problem with the given information: pressure (P­), density (r) and acceleration due to gravity (g). We have a simple equation connecting the height (unknown) with these quantities: P = r g h.  On using this equation and the values, one gets an answer of 10 m which is one of the choices.  Fortunately or unfortunately, this is the right answer with a wrong approach!

What the student missed is the right analysis of the question.  What the evaluator missed is the student’s wrong analysis for the right answer.  There are many such instances of obtaining a right answer by a wrong approach and analysis.

So what is the right approach to this question?

Using the information given in the problem and using the Boyle’s law (as Temperature is a constant): P1 V1 = P2 V2; here P1 = Pa+Pw; Pa = atmospheric pressure, Pw = pressure under water at a depth h; and Pw = r g h; P2 = Pa; V1 = Vo; V2 = 2 Vo.  Solving the above equation you get Pa = r g h, which when substituted for the given values yields 10 m for the height!  This is the right answer with the right approach.

In such a situation, how will the student know that his approach was wrong? When many are settling for the right answer, why would anyone ‘worry’ about the right approach? If MCQs become the system of evaluation particularly in the middle and high school examination schemes; where students are striving to understand basic concepts with effort and clarity, the chances of rushing to conclusions regardless of the right or wrong approach are very high and this leads to adulterated learning. This is what worries me as a teacher.

I genuinely hope that students, teachers, examiners and educators understand the trepidation I have to this approach in evaluating students. Evaluations such as these should be carefully thought over, meticulously designed and most importantly validated by specialists of the tool (MCQs) itself.

– Dr. Srivatsa S K

Director, Research and Development

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One thought on “Spoilt for choice

  1. I agree Vatsa that the design of MCQs is a task to be taken seriously to avoid ambiguity of approaches in arriving at the right answer.
    It is a sad circumstance indeed when questions such as the one mentioned above appear in competitive examinations where the depth of subject knowledge is put to test.

    Like

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