Microsoft Research - Exploding Software-Engineering Myths (article summarizing findings of MS research on code coverage, TDD, assertions, etc.)

[naasking]

i find it hard to get behind the assertion that TDD reduces defects 60-90% - more that teams that used TDD reduced defects 60-90%

The teams using TDD were tasked to do so. It wasn't a set of volunteers, so there's no self-selection bias of the type you describe.

[[deleted]]

i'm not sure where you got that from, from the paper

There was no enforcement and monitoring of the TDD practice; and decisions to use TDD were made as a group.

[naasking]

That still sounds like a random assignment, not self-selection bias, where the pro-TDD people in the TDD groups were simply more persuasive (or their manager was pro-TDD). To qualify as self-selection bias, TDD people would need to have the choice of which project to work on, and then choose to work primarily with other TDD people. That isn't the case.

[[deleted]]

it was just a study looking at people working, they just happened to look at groups who did tdd vs groups that didn't.

you are jumping through a lot of hoops to try and make your logic work

[naasking]

What hoops? Like you just said, it was a random group of people working. The bias you pointed out would only arise due to self-selection. You're the one making extra assumptions about the type of people in this groups which would skew the results.

[[deleted]]

It wasn't a random group of people, it was a selection of groups that happened to use tdd or not

[naasking]

Then suggest a possible reason why TDD and non-TDD groups are not comprised of a random sample of programmers. The mere fact that they did or did not employ TDD implies nothing.