Comments on: All measurements are wrong

By: Joe Devon

Joe Devon — Fri, 08 Oct 2010 01:38:00 +0000

Ever watch House? Your title reminded me of his favorite saying: All patients lie.

By: Roland Bouman

Roland Bouman — Tue, 05 Oct 2010 19:14:04 +0000

Hi Baron,

do you mean “measurements are wrong because of measurement uncertainty”? If you mean the same measurement uncertainty as in science, then really, calling all measurements “wrong” is way over the top. It just means we can be sure up to a degree.

It does provoke an interesting discussion about how we can calibrate measurement instruments, and how we can gauge the amount of uncertainty. (Something i don’t have a clue about w/re computer instrumentation)

By: John

John — Mon, 04 Oct 2010 16:40:47 +0000

Another way to accurately describe that would be “The CPU usage is estimated* to be 70%.” Also you could call them “samples” rather than “measurements” so it is clear that they are not absolute. It’s good to be aware of the actual method by which such figures are generated, but you can also obfuscate the meaning by using overly descriptive language in general conversation. I had to read the correct definition twice to get it.

* Measured at centisecond resolution. See …

By: Xaprb

Xaprb — Mon, 04 Oct 2010 13:58:51 +0000

Measurement intrusion effect is one factor, and was proposed as an answer to Neil’s question by another audience member. But that wasn’t his point — his point was simpler than that technical detail. Measurements result in a quantity, but it isn’t the real quantity. A simple example is a process’s CPU usage. This is gathered by polling with centisecond granularity. It is not an exact measurement because the process of measuring is inexact, and the same is true of everything else we can measure.

By: Duane Gran

Duane Gran — Mon, 04 Oct 2010 13:24:05 +0000

True enough, but context matters. If you are working with real time systems then any instrumentation will contaminate the results. For most applications the cost of calculating time or writing the results to a log are negligible compared to the major processing being done.

Real time systems are the only examples that come to mind. Are there other systems where this would pose a significant problem?