[andylei]

efficiency = output / input

you can't measure efficiency by only looking at time spent. if the 80 hr a week guy produces twice as much as the 40 hour a week guy, their efficiency is the same. if the 80 hr a week guy produces 3 times as much, his efficiency is 50% higher

[aschepis]

Software engineers aren't making widgets, and its hard to measure output quantitatively. I can assure you that your ability to make good decisions isn't as good after 18 hours of working as it is during the first 6. In engineering, good decision making can save you tons of time in the long run.

[fullmoon]

But the assumption that an the very same guy produces twice the amount in twice the amount can't obviously be true in any job that requires mental exertion.