Are designed based stereological methods unbiased?

There is a common misunderstanding that design based methods are by definition unbiased. That is simply not true. There are those that have said to me, “It’s design based because I designed this idea. It is designed and therefore unbiased.” I think that latter comment tells you that being a designed based method is not necessarily unbiased. I realize that the person making the comment was unclear about the meaning of design based, but that’s the way it happened.

In a design based approach it is is possible to show whether or not a method is unbiased. It doesn’t mean that biased can’t creep in if the method cannot be implemented properly, but at least there is the hope that the biases introduced during the implementation of the method are not overwhelming.

You might ask yourself if bias if really all that bad. Does it really matter if a method used in stereology has bias? What is that doing to the result? If the amount of bias is small relative to the value being determined, then it might not be bad if the method is biased.

Suppose a method had a bias estimated to be less than 5% and the data showed a 20% difference between control and experimental, then the 5% is not important. The method would be a reasonable method if it saved work.

Unfortunately, biases are difficult to determine. Showing that the bias is less than a certain magnitude is usually impossible.

That is why design based methods that are unbiased are favored. If the method can be shown to have zero bias, then the issue is how close to the mathematical ideal is the implementation.

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