Make measurable: what Galileo didn't say about the subjectivity of algorithms

Galileo's aphorism "Measure what can be measured, and make measurable what cannot be" echoes through almost every algorithmic system today. But reverberating in these echoes is the reality that the act of'making' something measurable is never purely objective: it is the result of subjective choices. Acknowledging this is key to preventing the harms algorithms can create. It's seemingly intuitive to think of'data' about a thing as a true representation of it. For example, my height is 5'9" and London is the capital city of the United Kingdom -- two data points that reflect reality. But renowned statistician David Spiegelhalter reminds us how data'is almost always an imperfect measure of what we are interested in.' To count all the trees on the planet, he notes, we must first define what counts as a tree. There's more than one way to do that, and not everyone will agree on which way is correct. It's a good reminder: some would say I'm more like 5'8" and a half, depending on how you hold the tape measure, and what of Edinburgh, Wales and Belfast?