I probably articulated that poorly but my general thought is that in any urban area (the paper talks about Boston a lot) there is already going to be a fairly l

I probably articulated that poorly but my general thought is that in any urban area (the paper talks about Boston a lot) there is already going to be a fairly large amount of turnover/subletters. I've lived in ADUs in residential SFH areas and have subletted apartments. The 20% is arbitrary but I guess my general instinct is that because the baseline for turnover/short-term subletter in any area that is somewhat urban (the focus of the paper) is going to be 5-10% minimum. The 20% I admit I pulled out of my ass, but its hard for me to fathom how a 3% usage in AirBNB would be more impactful than an area that sees 20% year turnover and a 15% subletter rate.