Self-Tracking Basics: Minimizing Measurement Error

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quantified self personal analytics personal informatics tips theory and practice by measured me blogOne of the first “reality checks” that you have to accept when starting a self-tracking project is existence of measurement error. No matter how technologically advanced are the measurement and recording tools you are using, these instruments will never be able to capture the “true value” of the object or trait that you attempt to measure. Take, for instance, body weight. If you weigh yourself several times throughout the day, and then chart the results, you will notice considerable fluctuation. Your weight will naturally go up right after breakfast and even more after lunch, and your gym scales will most likely show different results than your scales at home. These differences are caused by so called “systematic” error.

This is an error that occurs due to the misuse of instruments and changes in measurement procedure. In the above mentioned example, you weighed yourself in different time of the day, using different scales, etc. Every time you introduce a change in the measurement procedure, you affect the results.

Luckily, systematic errors can almost often be eliminated or minimized by means of standardization of the measurement process. In other words, you fight systematic error by introducing the system: find the optimal conditions under which the measurement is assumed to be most accurate, and from now on stick to the same routine.

Another type of error that will always follow you on your self-tracking endeavors is the “random” error. This is a “noise” that occurs due to uncontrollable factors and nature of the object that you are trying to measure. I would say that the more intangible is the object, the higher is random error. For instance, latent characteristics such as emotions, mood and other psychological traits are the most difficult to capture. In this case, taking multiple measurements (or better, multiple instruments) and averaging out results could help to minimize the error.

Finally, remember: in self-tracking projects, it is almost always about relative comparisons. In other words, it is not the absolute value of whatever you measure that matters, but the relative change in its values across time periods or treatments. If you keep measurement routine the same, then you will still be able to capture the change. So even if your bathroom scale constantly underestimates your weight by 1 lbs, you will still be able to see your progress, as long as you continue using the same scale.

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One Response to Self-Tracking Basics: Minimizing Measurement Error

  1. life scientist says:

    Could not agree more! There is no such thing as a perfect measurement. Consistency and reliability of your instruments are the keys to success in any experiment. The electronic bathroom scales are especially notorious for inconsistent measurements (my personal experience).

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