The bugs which static typing eliminates are mostly quite trivial and when these occur in coding with a dynamic language, the programmer is likely to catch them, but wastes time in the process. The bigger advantage is then in terms of productivity. Also these test have been done on an analysis of a large number of existing projects: I wonder to what extent they have accounted for any tendency that larger projects (which will have higher complexity and therefore higher bug rates) will be chosen to be written using a statically typed language.

The great thing about the benefit of static typing though is that it comes for free. The author overstates the benefits shown by the TDD studies. Nearly all show an increased cost in the use of TDD generally around 10 to 15% of dev time. One would assume the improvements are mostly against not testing rather than post-testing, this isn’t entirely clear. Also the larger meta study showed a number of studies that were inconclusive or showed no improvement in defect density.