FUN FACT: the "bystander effect" is bullshit
during the first "studies" done into it, the test subjects knew it was part of an experiment... so that data is completely useless. more recent studies done using actual real scenarios recorded on security cameras show people will nearly always intervene unless there's a danger preventing them from doing so
@vantablack even if bystanders don't want to directly intervene for their own safety (such as a gang fight between a large group of teenagers/young adults who are using knives or other weapons) they generally *will* call 999/112 and will try and give first aid to anyone injured left over once the combatants have fled until the Ambulance arrives...
"bystander effect" may be an issue in countries where too many sketchy folk have guns and others are frightened of being sued if they help someone..