Alan Marco (USPTO Chief Economist) and Richard Miller (USPTO Senior Economist) have recently posted Patent Examination Quality and Litigation: Is There a Link?, which compares the characteristics of litigated patents with various matched controls. The litigation data was from RPX, the patent data was from various USPTO datasets, and the controls were either chosen randomly from the same art unit and grant year or were chosen with propensity score matching based on various observable characteristics. They are interested in whether examination-related variables that can be controlled by the USPTO are related to later litigation, and they conclude that "some examination characteristics predict litigation, but that the bulk of the predictive power in the model comes from filing characteristics."
Marco and Miller report that patents filed by small entities are more than twice as likely to be litigated than those filed by large entities, and patents with longer continuation histories and application pendency are also more likely to be litigated. Government-interest patents and foreign-priority patents are much less likely to be litigated than other similar patents. Other characteristics that indicate higher probability of subsequent litigation include having more independent claims and shorter independent claims (proxies for broader patents), being allowed by examiners with signatory authority, not being allowed on first action, having more IDS filings or examiner interviews.