The Necessary Bell Curve: Why & How

Singaporeans face the bell curve from the age of 12 and this may continue all the way till we retire. It is used in nearly all national exams including the PSLE and also in firms where they mark employees for promotion / firing. There is a natural reaction to simply call this measure brutal and unnecessary but I hope to show why the bell curve is necessary and whether it is ‘good’ or ‘bad’ depend only on how and why it is used.


What is the Bell Curve?

The bell curve is a graph that dictates a simple relationship. It measures the number of people found in each group. These groups are measures of abilities.

Bell Curve: Most are average, only a few are special

Bell Curve: Most are average, only a few are special

As the shape suggests, a huge number of people are found in the middle group. And there are groups on the extreme ends which hold smaller numbers of people. It’s intuitive and technically proven, the majority of us are average joes found in the middle group and then there are the less able and the tremendously gifted – tiny proportions found at either ends.

The bell curve is used aggressively due to such properties. It is used to differentiate people no matter the score.  Take for example a class where everyone scores above 85/100. There will be very few who score 85-87, and also 98-100. The bulk will fall between 88-97. The bell curve will grade this distribution of results accordingly.


The bell curve helps to differentiate groups no matter how close they are.


By definition (in my time at least), a score of 85 and above is considered Band 1. With the bell curve, the grades shift according to the students. In the example above, probably 97-100 will be graded Band 1, 94-97 a Band 2, 88-93 a Band 3 and 85-87 a Band 4.

Of course, this is just a guide. Some grading departments may decide it is too harsh to put a child who scores 85 in a failing band but this is entirely up to them. The bell curve helps to differentiate groups no matter how close they are.


A Necessary Evil

The example I showed above is probably skewed upwards but it is very real. You may score well enough on absolute grades (hey 50/100 is a pass isn’t it?) but do poorly because your peers simply did better. Your absolute grades are not important, your relative performance is. Now this sounds extremely cruel isn’t it? Unfortunately, it isn’t.

Students feared the bell curve so much that they offered tidbits to it.

Students feared the bell curve so much that they offered tidbits to it.

I’m not writing as a person who is on the elite end of the spectrum. Yours truly is an average Singaporean who has been handicapped by the bell curve in national exams. Of course, there are times when the bell curve aids me but most of the time, it is more of an enemy than a friend. But not all enemies are bad things and the bell curve is a necessary ‘evil’.


Imagine a world without a bell curve.


Imagine a world without a bell curve. Two things will occur, either the top end of the ability spectrum will balloon (everyone passes/scores an A based on absolute scores) or examiners / assessors will have to be very quick in adjusting their exams / tests to adapt to the cohort. Neither is a scenario we need. We won’t know who are the academically inclined without the bell curve. We won’t be able to identify qualified people for crucial jobs. The very structure of society will be blurred because there are no margins – just simple lines that everyone crosses with ease.

Losing its Essence: Everyone gets a Trophy

Losing its Essence: Everyone gets a Trophy

To bring the above in the hotly debated PSLE context – how would you feel if your child scored 4 A*s, and so did every other child in Singapore? How would you tell the school of your child’s choice that he/she should qualify for it?

The bell curve is only as cruel as life is. Not everyone is created equal. Not everyone is equally talented. The bell curve is just a tool that helps us to sort (rather clinically) students, employees, citizens, etc. Without this tool, a country’s growth will be affected terribly.


The bell curve is only as cruel as life is. Not everyone is created equal. Not everyone is equally talented.


Proper Use of the Bell Curve

The main question is not whether the bell curve should be used but rather how such a crucial tool should be employed. I hope the above explains why we cannot simply junk it. Here’s how I think the bell curve should be used:

  1. Bell curve when the spectrum is too wide. When the cohort demonstrates a very wide ranging set of abilities, the need to differentiate and classify increases. It will be a failure on the assessor’s end to not effectively classify the group. If everyone is close in ability, there is no reason to bell curve. In most local universities, bell curving stops being used at will for undergraduates in the honors year. In some companies, bell curving halts when one reaches the upper ends of corporate hierarchy  This is because people in those groups are already very closely matched and any attempt to differentiate these will yield groups that do not differ much at all.
  2. Use it when there are too many people for very little spots. Sometimes, it is unfortunate the scarcity enforces the use of the bell curve. If you have a pool of 300 candidates and only 10 spots for them, it doesn’t matter that these 300 candidates are close in ability – you still have to pick 10. Randomly picking is not an option, you will have no choice but to bell curve this tight cohort and pick the top 10. Scarcity increases the need to pick very specifically. Everyone has to work with their constraints.
  3. Use only the upper end of the bell curve. Some companies like Microsoft and GE demonstrate a lack of knowledge in using the bell curve. They bell curve under all situations. This means they fire every year for the sake of firing. This is a poor way of using the bell curve. The moment the spectrum is no longer wide and the institution is satisfied with the base level of its cohort, the bell curve should only be used for promoting top performers and not eliminate base liners. If your base talent is good enough, firing them will be a stupid move.
  4. Be sensitive when bell curving children. A bell curve is a fancy, more technical and descriptive term for an assessment. How early we should subject our children to such forms of pressure is up in the air. It varies by countries and by culture. There is no right or wrong to this. Doing it early may help to spot and nurture early bloomers but impede their late counterparts. It’s a messy topic for another time but the issue is not whether to bell curve but when and how to carry it out.
PSLE: It's not how but when

PSLE: It’s more about timing and execution



You don’t bell curve for the sake of bell curving, you bell curve only when it is absolutely necessary. Some have called bell curving the creation of scarcity. If it is used that way then it is a poor use scenario. The bell curve is a tool that responds to conditions, not create them.

As much as a knife should never be blamed for a murder, it is the wielder that should be held responsible for whatever outcome the bell curve produces.

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