Professors Stephen J. Choi and A.C. Pritchard have recently published a study finding that private securities litigation provides as a greater deterrent effect on securities fraud than do SEC investigations — when only one or the other has been filed.  The study also finds that the best outcome for investors is when there are parallel SEC investigations and private securities litigation.  Choi and Pritchard, SEC Investigations and Securities Class Actions: An Empirical Comparison, New York U. School of Law, Law & Economics Research Paper Series Working Paper No. 12-28 (December 2012).