(I say the following from my own early experience with Marshall having met Marshall in1972, taking my first workshop in 1973 in St. Louis, Missouri, signing the articles of incorporation of CNVC in Dallas, Texas in 1984, along with two others including Gloria Rosenberg).
Virtually all conflict resolution programs have an academic setting as their foundation and therefore have empirical studies by graduate students assessing their efficacy. NVC is remarkable for its roots. Marshall Rosenberg, Ph.D. (clinical psychology, U of Wisconsin) comes from a full time private practice in clinical psychology and consultation, never an academic post. NVC, his creation, is entirely a grassroots organization and never had until recently any foundation nor grant monies, on the contrary funded 100% from trainings which were offered in public workshops around the world. Literally in its first 20 years Marshall Rosenberg drove his car around the US from city to city where private individuals and groups asked him to come to offer training. NVC was developed from the "foxholes" when Dr. Rosenberg under a federal grant was mediating school desegregation disputes in the South during the late 1960's. It was born out of violent and deadly conflict and continues to be offered in such places around the world; although it is most frequently taught to individuals and groups seeking help with everyday garden variety conflicts with their spouses, children, parents, neighbors, co-workers, bosses, etc. Empirical data is now coming slowly as independent researchers find their own funding to conduct and publish empirical studies with peer review.
[written to the CNVC Trainers list, Sept 20, 2011]