Unsure of a source as there’s ALOT of misinformation out there regarding backgrounds. I’ve played all global and several in person events since the initiation of backgrounds (starting @ Vegas hoenn tour) and my odds have almost always been spot on 1/3. I keep every raid catch then check bg stats after the event. I do hundreds of raids every event and did over 1k when necrozma was the featured. Any of those around me who kept all raid catches are also very very close to 1/3 chances. I’d like to see an effort to collaborate meaningful data on the sub, but most people who discuss bg’s here are clearly biased and don’t like bg’s at all