Read up on Project Management. You're looking for Scope, Schedule, and Budget, in particular the S curve. You should be able to plot % complete against % spent for a sampling of projects, and demonstrate where the projects went off the rails. Then you can figure out why.
Usually it's because the scope was not well defined. and thus budget and schedule were not based on a realistic assessment of what it takes to achieve said scope.
And yes, I provide training for exactly this. A neat little tidbit:
Q: Of 700+ projects in a study, how many recovered once they were over budget at 15% completion? That is, if a job was over budget at the very beginning, what are the chances of completing it on time and within budget, based on 700+ projects?
A: None. Not a single job.