The McNamara Fallacy is a common problem in research. It happens when researchers take a single piece of data as evidence that their hypothesis is true. 

This can lead to flawed and misleading conclusions.

In this article, we will go over how to avoid the McNamara Fallacy through proper research design and execution.

What is the McNamara Fallacy?

The McNamara Fallacy is a cognitive bias that occurs when trying to make sense of data. In this case, the data refers to your own beliefs and values.

The McNamara Fallacy is a common problem in research. It’s also known as the “Measure what you can measure” fallacy, and it’s an easy way to get bogged down in analysis paralysis. It can happen when researchers are not sure whether something they’re studying should be measured or not, so they just measure everything they can get their hands on in hopes that some of it will turn out to be important.

The fallacy is named after General Robert McNamara, who was the United States Secretary of Defense during the Kennedy administration. Robert, an early adopter of the Quantified Self ideology, believed that by managing some military statistics, he could win the Vietnam War.

The problem with the McNamara Fallacy is that it often leads you to believe that you have a clear understanding of the world and how it works when in reality you only have a vague idea of what’s going on. Just as in the case of Robert McNamara who confused measurability with relevance.

For example, imagine that you’re researching the effects of different types of exercise on your body. You’ve decided to do one type of exercise for 4 months and then switch it up for another 4 months. You’ll be able to see if any differences emerge between the two types of exercise.

If you do this experiment wrong (and all researchers do this at least once), your results will be inconclusive because you haven’t defined what “success” means in this experiment. You just wanted to see if any differences emerged between the two types of exercise over time.

Examples of the McNamara Fallacy 

The McNamara Fallacy is the result of a belief that you can measure performance in education but not learning. This happens when people are so focused on results that they miss the bigger picture. For example, “Education”.

Oftentimes, researchers try to measure what students have learned by administering tests Or assessments, but they don’t ask students to do anything that helps them imbibe what they have learned. 

That’s why you might see a study that says, “We found that students who did this test scored better on the test.” But you also might see a study that says, “We found that students who did this other test scored better on the test.”

But there’s a problem with this approach: You can’t measure learning with a test. You can only measure how well someone performed on a test. And when you’re looking at how well someone performed on two or three different tests, it’s hard to tell which one was more important or even if it mattered at all. You may be satisfied with the result but your research is biased.

Another example is if you were conducting a study on how water affects the quality of life in developing countries, you would have to consider how clean water might affect those people’s quality of life. That might not be something you could easily measure and so it’s easy for you to overlook the fact that it might not actually be important or relevant to your research.

Other examples: 

  • When evaluating teachers, we focus on standardized test scores instead of how well students learn. 
  • When evaluating teachers’ decisions, we focus on whether or not it was effective rather than asking what it meant for students’ ability to learn.

Just as there are many types of fallacies, there are also many ways to detect and avoid them. We will be looking at those ways in the following paragraphs.

How To Detect the McNamara Fallacy 

The McNamara Fallacy is a common problem among researchers. It is a situation where researchers measure what they can easily measure, and then ignore the rest of the universe. 

This fallacy occurs when a researcher assumes that what cannot be measured easily does not exist and that what can be measured easily is important. The McNamara Fallacy is especially prevalent in research involving human subjects. 

For example, researchers may study the effects of a drug on patients and assume that the patients who experienced side effects would not have done so without the drug. However, it’s easy for researchers to forget about those patients who did not experience side effects because they were too busy feeling good during their study visits or could not tolerate the side effects of a drug due to other health problems.

To avoid this pitfall, researchers should always remember that there are many factors that affect how well a subject responds or reacts to something and these factors can often be more important than what happens during the experiment itself. There are many ways to detect this fallacy in research. 

One way is to use an experiment that measures all variables, including those that cannot be measured easily. Another way is to have your data analyzed by someone who knows how to analyze data from areas where it is hard to measure things like happiness or productivity (as opposed to areas where it’s easy to measure things like productivity). 

How To Avoid the McNamara Fallacy 

In order to avoid the McNamara Fallacy, researchers must be aware of how their results are influenced by their measurement methods and how those methods affect the results they get. 

The best way to avoid this fallacy is by asking yourself these questions: “What am I trying to accomplish?” “Who will be affected by my study?” and “How will they be affected?” 

If you answer these questions carefully, you’ll find that your studies will be more likely to focus solely on how people learn rather than what they perform well at or not so well at.

An obvious way to avoid this fallacy is by taking a look at what you’re measuring. If your study isn’t focused on learning, then you’re probably measuring performance instead of learning. 

For example, if your study focuses on how many students are doing well in math or reading compared with other students at your school, this is an example of the McNamara Fallacy because it’s focused on performance instead of learning.



What if you don’t have any right answers? What if your data isn’t usable? What if your sample size is too small? What if you don’t have any time to analyze all that data? The McNamara Fallacy says that all these things shouldn’t matter, that you should just measure as much as possible and then make judgments about which results are useful.

But this is wrong! You need to do more than just measure; you need to use your measurements to better understand the world around you, and only then will we be able to develop theories about how things really work.


  • Emmanuel
  • on 5 min read


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