Why proxy measures stand in for hard to count change
Launch library · evergreen read
A proxy measure is something more easily observed that is used to stand in for a harder to directly measure outcome, chosen because it is believed to move alongside the real thing even though it is genuinely not the real thing itself, only a convenient stand in for it that makes measurement practically possible.
Proxies are useful precisely because some genuinely important outcomes cannot be measured directly at reasonable cost, but their usefulness depends entirely on how closely they actually track the outcome they are meant to represent, which is worth checking regularly rather than simply assuming forever without ever revisiting it.
Campaigns that rely on a proxy measure should stay alert to situations where the proxy and the real outcome start to diverge, since chasing a proxy that has stopped reflecting the underlying reality can quietly lead a whole campaign astray without anyone noticing at first, sometimes for a considerable stretch of time.