Friday, 8 July 2011

A question of measurement

As stated somewhat flippantly in last week's post, the mystery of quantum effects is in my opinion, a question of measurement. Besides uncertainty, there is this problem with the observer, whereby the observation of a quantum system somehow resolves it's probabilities into actualities. This implies that measuring a system determines the state of that same system. If the system-to-be-measured, is not the system-once-measured, what do measurements mean?

It's a topsy-turvy world down there at the quantum level.

But all is not necessarily as it seems at the macro level either. Think of taking the temperature of a volume of liquid using a mercury thermometer – the thermometer generates a reading because there is heat exchange between the liquid being measured and the thermometer. The act of measuring has changed the system, however slightly. For many purposes the thermometer can be regarded as accurate; the change in temperature that the thermometer effects in the liquid is negligible compared to the smallest unit of measurement.

At the quantum scale however particles are so small and travel at such high speeds (close to the speed of light) that even the infinitesimal is not negligible. This makes it basically impossible to take any measurements without significantly altering that being measured.

Complex adaptive systems display the same resistance to objective observation; for instance, it's notoriously difficult to measure the behaviour of human beings without modifying the behaviour under observation – have you ever dear reader suffered a blackout when taking an exam? Another example is the stock market; measuring consumer confidence can lead directly to a dampening or buoying of the market. Otherwise there is the stock indication itself - the very fact that stock is falling is often the reason that it continues to fall (or rise and rise as the case may be).

But doesn't that make an empirical approach to anything inherently problematic? Well, yes, but it's like Churchill reputedly said of democracy; it's the best we've got! There are steps that can be taken to reduce the subjectivity of a given observation or measurement and its impact on the system being measured, experiments can be set up whereby measurements approach objective non-invasive observations. This is an arduous process, which can be deceptively difficult to get right, and it breaks down quickly in the face of complexity.

How should we mere mortals effectively inspect (let alone adapt) then in the wonderfully complex arena that is software development?

We should proceed with care, measure only the bare minimum and always interpret metrics as approximations, avoid false precision. We need to recognise that metrics will drive behaviour, and be on the lookout for how. The measurements we do decide to take, we can make as trustworthy as possible by keeping as many other important variables as stable as possible. Measuring in relative quantities also helps, as does changing only one thing at a time. In short; apply a light weight version of the scientific method, remember Occam's razor and, be humble!

For example; to make velocity measurements meaningful/useful (for planning purposes), we should fix the sprint duration and keep the configuration of the team stable. We should estimate in story points and include only the points for completed stories in our measurements. Even having done all that, we should allow for the imprecision of our measurements by predicting only on the basis of velocity ranges.

Further we should remember that, while measuring team velocity can have the side effect of driving performance, measuring individual 'velocity' will have a detrimental effect on the team's results – especially if it's a manager doing the measuring!

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