In Peopleware DeMarco and Lister explain the Gilb Measurability Principle by what they call Gilbs law:
"Anything you need to quantify can be measured in some way that is superior to not measuring it at all."
That does not mean that it will be easy, cheap or perfect, only that it will be better than not measuring.
Tom Gilb:
"Sometimes, it seems difficult to identify satisfactory scales of measure. Often, the only ones that can be found are indirect, imprecise, and have other problems associated with them. From my point of view, these problems can be tolerated. The specific scales of measure, and meters for measuring, can always be worked on, and improved over time. In all cases, an attempt at quantified specification is better than vague words."
I agree with Gilb's law, and I measure a number of things on projects I lead. However, there is a difference between measuring things that are indirect and imprecise and measuring productivity.
So I disagree that productivity can be measured, but agree that there are things you can measure and agree that measuring those things is valuable.
In the quoted example, Joel's eigth test measures the environment for interruptions. This is a good thing to measure. However, this is not the same thing as measuring productivity, because then we jump to the conclusion that "Working alone in an office with a door is more productive than pair programming because pairs interrupt each other constantly."
So, my thesis is that you can and should measure lots of things, but if you are not directly measuring productivity it is misleading to pretend that you are.
In Peopleware DeMarco and Lister explain the Gilb Measurability Principle by what they call Gilbs law: "Anything you need to quantify can be measured in some way that is superior to not measuring it at all."
That does not mean that it will be easy, cheap or perfect, only that it will be better than not measuring.
Tom Gilb: "Sometimes, it seems difficult to identify satisfactory scales of measure. Often, the only ones that can be found are indirect, imprecise, and have other problems associated with them. From my point of view, these problems can be tolerated. The specific scales of measure, and meters for measuring, can always be worked on, and improved over time. In all cases, an attempt at quantified specification is better than vague words."