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What Is A 'Proxy'? (Measurement)

A Proxy measures one quantity by measuring something else. Think of votes: they measure the "will of the people", although measuring it with 100% accuracy is impossible.

The closer the Proxy to the related subject, the more accurate.

Proxies can help measure the immeasurable, but you have to make sure that the Proxy is highly Correlated with the subject of interest.

Josh Kaufman Explains 'Proxies'

What do you do if it's not possible to measure something directly? A Proxy measures one quantity by measuring something else.

For example, in democratic political systems, votes are used as a proxy to measure the "will of the people." It's not possible to subject every citizen in a country to a brain scan that reveals detailed preferences, so votes are used as the Next Best Alternative.

Proxies are used all the time in scientific measurement.

Ever wonder how scientists know how hot the sun is, or how old certain rocks are? They measure proxies like the wavelength of electromagnetic rays or the decay of known radioactive isotopes, then apply well-proven relationships and formulas to determine the answer.

Useful Proxies are closely related to the primary subject-the closer, the better. Take Web site analytics-you may want to know exactly where and how long people pay attention to different parts of the Web page, but again, you can't brain scan each visitor to your Web site.

Tracking the position of the mouse cursor, however, can be a useful proxy for attention. According to a study done by Carnegie Mellon University: "...84% of the times that a region was visited by a mouse cursor, it was also visited by (users') eye gaze.

In addition, 88% of regions that were not gazed by the eye were also not visited by a mouse cursor." Because mouse movements and eye fixation (i.e. Attention) are highly correlated, mouse movements are a good proxy for visitor attention.

The better the Correlation, the better the Proxy. For best results, ensure the proxy is actually related to the intended subject.

Proxies can be tricky or misleading if they seem to measure one thing, but actually measure another. Think back to the example of trying to measure programmer productivity by counting lines of code as a Key Performance Indicator.

As we discussed earlier, "lines of code" is certainly a Proxy for programming effectiveness, but more code is sometimes an inverse signal of productivity, making it a useless measurement for the stated objective.

Used with care, proxies can help you measure the immeasurable-just be sure your proxy is directly and highly Correlated with the subject of interest.

Questions About 'Proxies'

• If you're having trouble measuring something, could you measure something else that's related to it?
• What proxies could you potentially use to triangulate into a better understanding of your subject?

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"How many legs does a dog have if you call the tail a leg? Four. Calling a tail a leg doesn't make it a leg."

Abraham Lincoln

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