Schedule estimation and uncertainty surrounding the cone of uncertainty

Software development project schedule estimation has long been a difficult problem. The Standish CHAOS Report indicates that only 20 percent of projects finish on time relative to their original plan. Conventional wisdom proposes that estimation gets better as a project progresses. This concept is sometimes called the cone of uncertainty, a term popularized by Steve McConnell (1996). The idea that uncertainty decreases significantly as one obtains new knowledge seems intuitive. Metrics collected from Landmark's projects show that the estimation accuracy of project duration followed a lognormal distribution, and the uncertainty range was nearly identical throughout the project, in conflict with popular interpretation of the "cone of uncertainty"