Evolving Error Profiles and Activity Proportions with Project Scale

Key Insight

Both the quantity and type of errors shift significantly with project size. On small projects, construction errors account for approximately 75 percent of all errors found, where the skill of the individual programmer is the primary influence on program quality. As projects grow larger, construction errors typically decrease to about 50 percent of the total, with requirements and architecture errors making up the difference due to increased complexity in these earlier phases. However, in some very large projects, construction errors can still account for up to 75 percent of the total, even with 500000 lines of code.

Error density, defined as the number of defects per 1000 lines of code, escalates non-linearly with project size; a project twice as large is likely to have more than twice as many errors. Typical error densities range from 0-25 errors per KLOC for projects smaller than 2K lines of code, increasing to 4-100 errors per KLOC for projects 512K lines of code or larger. This data shows that very large projects can experience up to four times as many errors per KLOC as small projects, requiring significantly more effort to achieve comparable error rates.

The proportion of development activities changes dramatically as projects scale. On small projects, construction is the most prominent activity, consuming as much as 65 percent of the total development time. For medium-sized projects, construction remains dominant but its share of the total effort falls to about 50 percent. On very large projects, architecture, integration, and system testing take up more time, leading construction to become a smaller, less dominant part of the overall effort, as other activities increase at a non-linear rate while construction scales more proportionately.