A friend (and former boss) wrote to me asking for an estimate of my average productivity per month in terms of raw lines of source code. I complied (source code control systems are great for mining this sort of information), but also started thinking about this metric.

We all know it’s a blunt instrument, full of caveats and gotchas:

• How do you compare different languages? 100 lines of COBOL equals 5 lines of Python.
• How do you compare different programming tasks? Implementing multithreaded database access with transaction support takes more care than writing diagnostic logging utilities.
• How do you compare different phases of the project? The end game requires slowing down the coding and taking far more care with every change.
• Do you only count lines created, or do you include lines changed? The same line can be edited many times in a month. Which programmer gets the credit?
• How do you deal with someone who spends a good chunk of time mentoring?
• Do you count comment lines? (Of course you do: they are an important part of writing software.) Do you count blank lines?

Even once you get past all these details, do you even want higher numbers? I once worked with an engineer who was clearly the most productive guy on the team in terms of lines per month. He also had a reputation for writing buggy, poorly designed code, and was difficult to communicate with. The whole team would have been better off if he had slowed down, thought about each line a little bit more, written fewer lines each month, and talked to everyone more often.

You have to be careful what you wish for. We all know that if you impose strict metrics on people, they will organize their work to maximize the metric. An extreme example: I heard a horror story years ago about a disk drive manufacturer that was having difficulty meeting their shipment quotas. The manager made it clear that he wanted the quotas met, and didn’t want to hear any bad news. In desperation, they started shipping boxes with bricks in them instead of drives, or so I was told. Maybe it’s an apocryphal story. But it has the ring of truth to it, and all of us have been in situations that smelled a little bit like that.

I don’t think we’ll ever get away from the lines per month metric. It’s just too easy to compute. The best we can do is take it all with a huge grain of salt, and use it as one piece of information alongside many others.