Was able to get the site to load after several tries, which has led to a humorous juxtaposition with the comments here. Other commenters are saying that they know what drives software costs, and while I agree with some of the comments, there's also stark irony as the linked research is explicitly aimed at trying to debunk "gut feeling" about correlated data that leads to higher costs and discover causation data:

>> "If we want to proactively control outcomes, we would be far more effective if we knew which organizational, program, training, process, tool, and personnel factors actually caused the outcomes we care about. To know this information with any certainty, we must move beyond correlation and regression to the subject of causation. We also want to establish causation without the expense and challenge of conducting controlled experiments, the traditional approach to learning about causation within a domain. Establishing causation with observational data remains a vital need and a key technical challenge."

>> "Armed with this new approach, we are exploring causal factors driving software cost within DoD programs and systems. For example, vendor tools might identify anywhere between 25 and 45 inputs that are used to estimate software development. We believe that the great majority of these factors are not causal and thus distract program managers from identifying factors that should be controlled."

Since down, didn't read: Don't assume you know the answer. The point of the research is to prove what's actually a causal driver of costs, not just an unrelated correlation winking suggestively at it.