Curves

I’ve been following a loosely coupled weblog discussion about using curves when grading, doing performance reviews, etc.

It’s being discussed by Paul Vick here. Chris Anderson talks about it here and here. It all started from John Porcaro’s entry here.

Here’s my thoughts on this.

I think people are discussing different issues without realizing it. One issue is the idea of ranking people and using a curve to do the ranking. The other issue is the automatic application of the ranking to consequences, such as failing a class or being fired.

Clearly, John Porcaro is arguing against the automatic application of the ranking. I agree that automatically firing people simply because they rank the lowest is a bad policy. In my opinion, the key problem with this is that you have applied the curve to a unrepresentative sample.

Let me use a hypothetical example of what I mean by an unrepresentative sample. A sales manager has a sales force of 100 people. A performance curve is applied using various parameters. Using a curve, we assign the label “Good ” to the top 10%, we assign the label “Acceptable” to the middle 80% percent, and we assign the label “Poor” to the bottom 10%.

To automatically fire the bottom 10% and give bonuses to the top 10% is foolish, in my opinion. The sample only ranks the salespeople within the company. If you were to rank both your salespeople and all potential replacements, then I think you have a sample that is fully representative. If some your current salespeople fall in the bottom 10%, you fire them. Replacement salespeople who fall in the top 90% are hired. If all the replacement candidates fall in the bottom 10%, you don’t fire anybody.

Practically, it is very difficult to rank the replacement candiates along with the existing salespeople. It’s hard to compare apples to apples in this scenario. The ranking process is subjective. This subjectivity is why automatic application of rankings is bad.

I also agree with the argument that grade inflation is a problem. It is a problem that exists in our schools and even exists in some companies. I could argue that the problem of ranking inflation in a company solves itself when the company goes out of business, but I’ll leave that argument for another time.

Grade inflation is a problem, but automatic application of a curve is not the solution. The main problem with an automatic curve is that it creates a variable standard for passing. Take two classes learning the same material and give them the same tests. One class is an honors class. The bottom student in that class demonstrated a knowledge of 85% of the material. That student fails. The other class is regular students, the top student in that class demonstrated a knowledge of 85% of the material. That student passes, as well a bunch of students who understood less than 85% of the material. The “bar” in each class was set at a different level.

So what do we do? We set a standard of measuring achievement, and we stick to it. If it means that a class has 90% of the students getting an A, that is fine. If it means that 90% of students in a class fail, that is fine, too. Where we fail is in adjusting the bar down when it is not warranted. Another place we fail is not raising the bar when it is warranted.

Grade inflation is not a failure of those being ranked/measured. It is a failure of those doing the ranking. Applying curves is a popular solution because it is easy to do and it removes responsibility from those who have to do the ranking. You don’t like that you were fired? It’s the policy of the curve.

I could probably write a couple chapters in a book on this topic. I’ll stop here…

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