I heard of a study recently that concluded inexperienced and experienced programmers write about the same number of lines of code per day. The difference is that experienced programmers keep more of those lines of code, making steady progress toward a goal. Less experienced programmers write large chunks of code only to rip them out and rewrite the same chunk many times until the code appears to work. Or instead of ripping out the code, they debug for days on end, changing one or two lines at a time, almost at random, until the code appears to work.
As Greg Wilson pointed out in his interview, focusing on quality in software development often results in increased productivity as well. More effort goes into forward progress and less goes into re-work.
Not only do experienced programmers produce more lines of code worth keeping each day, they also accomplish more per line of code, sometimes dramatically more. But that’s not news. It’s well known that the best programmers aren’t just a little more productive than average, they’re one or two orders of magnitude more productive. (See, for example, Joel Spolsky’s book Smart and Gets Things Done.) More interesting is that the best programmers don’t seem to have a much larger capacity for producing and understanding lines of code.
There have also been studies that show programmers produce about the same number of lines of code per day independent of the language they use. You might think that someone working in assembly language could produce more lines of per day than someone writing in a higher level language such as VB or Java, but that’s not the case. It seems that while counting lines of code is a terrible way to measure productivity, it is a good way to measure what you can expect someone to be able to hold in their head.