[ckastner]

I briefly glanced over the paper, and in references to the 171 projects studied, the following stood out:

> The projects were mostly of short duration and small to medium size. The median project began in 2012 lasted 61 days, produced 4,200 Lines of Code, 49 components (modules or features). Duration ranged from 7 to 1,918 days. Size ranged from minimal (this may represent a short maintenance project) to 88,394. The earliest project was in 2006 and the most recent in 2014.

And from Fig. 11:

> Team size (median): 6

I suspect that a sample of projects involving larger teams, or a larger codebase, would have produced a somewhat more pronounced effect.

Furthermore, it is not clear to me what domains these projects where from (but I admittedly only skimmed the article). In the financial industry, for example, the defect cost increase is certainly more pronounced.