A few questions for the study:

1. What’s the data source? If they’re just doing news reports and traditional history that can hide a lot of failed non-violent protests. A non violent protest, especially one against the medias interests, is way less likely to show up in the historical record then a violent insurrection. Only the successful movements like the civil rights movement will get mentioned on the non-violent side whereas every insurrection or riot, successful or not, is captured in the historical record.

2. What’s the breakdown by method? It seems they’re including strikes in this which has a very high success rate and high occurrence, so much so it could drown out all the failed protests.