Also, quite possibly: day of month (contrast a week before payday vs just after), temporary local events and conditions (high unemployment one year vs the previ

Also, quite possibly: day of month (contrast a week before payday vs just after), temporary local events and conditions (high unemployment one year vs the previous), and if the wallet contained a tourist's details: the level of 2nd language knowledge predominant in the country (e.g. the old lady in one of the first slides probably didn't speak English, meaning a barrier to contact or an opportunity for a second individual to pocket the wallet). Overall though, if you randomised the drops nicely, increased sample size and repeated them a few times, it might be an interesting study.