Bigger projects tend to be more complex, so it's not surprising that they are more prone to cost overruns. They also tend to overrun by more, in dollar terms, and often in percentage terms as well (Figure 2.1).
The relationship between project size and overruns is not new. In 2014 Danish economic geographer Bent Flyvbjerg coined 'the iron law of megaprojects: over budget, over time, over and over again'.68 Our 2016 report found that a 10 per cent increase in project size (measured by cost estimate when first under construction) was associated with a 6 per cent higher chance of a cost overrun.69
____________________________________________________________________________
68. Flyvbjerg (2014, pp. 9-11).
69. Terrill and Danks (2016, p. 31).