Variability: responders, context and noise?

Life is messy – with many things happening all at once. The response to any given stimulus often depends on interactions with other parameters, not all of which can be measured with great accuracy nor are necessarily very stable. It is therefore understandable why consistent and predictable responses can be elusive, even when making repeated measurements under seemingly standardised conditions. Indeed, variability in observed data should be expected both due to measurement error surrounding the true value and due to natural oscillations in what value is actually “true” at any given time.