Type four error | “Error of the fourth type”

In statistics, we often talk about Type I or Type II error. Where Type I is a “false positive”, when we reject the null hypothesis when it is true, and Type II is a “false negative” when we accept the null hypothesis when it is false. These are statistical errors. Then there are the less talked about Type III (or even Type IV) error, which is human error that could happen to non-statistical problems.

In 1957, Kimball published “Errors of the third kind in statistical consulting“, stating that the error of giving the right answer to the wrong problem is a Type III error. He illustrated that this scenario could often happen in a consultant-client relationship. Similarly, in Decision Analysis (Raiffa, 1968) also describes a Type III error as correctly solving the wrong problem.

So a Type III error, in general, is the error in identifying the correct problem. Or, giving the wrong conclusion because the question was wrong to begin with.

Then, in ‘ Dirty Rotten Strategies,  Mitroff & Silvers proposed the Type IV error, which is when someone deliberately chooses to solve the wrong question in order to mislead people. So it is a Type III error + malicious intent.

In science, there are methods designed to avoid Type I/II errors. But in life, it is up to us on whether we commit error of the third and fourth type. We should be careful in what questions/quests we choose to solve. It is similar to the concept of knowing which battle to pick, because 1) not all of them is worth it, and 2) not all battles will lead you to the overall victory.  It is also crucial to reflect on our intent when making strategical moves. The line between being strategic and malicious are sometimes very fine.


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