Nonviolent protests are twice as likely to succeed as armed conflicts – and those engaging a threshold of 3.5% of the population have never failed to bring about change.
Also what these articles always fail to consider: Usually protests become violent when peaceful protests have failed. So violent protests often face something that is much harder to change/politicians are more unwilling to change. So of course they are less often successful. Not because they are less effective, but because the nature of their demands is different.