The "how many arrested" statistic is completely useless because the level to which marijuana possession results in arrest varies wildly between countries and even states or cities. Equally the frequency of searches, the criteria for selecting people to search all vary wildly.
Anecdotally, marijuana usage was much more prevalent amongst students I knew when I lived in Canada than it is in the UK. My experience (admittedly while travelling through) in the US was similar to Canada. This drug-use map[1] corroborates that (US 14%, Canada 12%, UK ~7%), although I do agree that any survey about drug use will probably not see completely truthful answers.
Anecdotally, marijuana usage was much more prevalent amongst students I knew when I lived in Canada than it is in the UK. My experience (admittedly while travelling through) in the US was similar to Canada. This drug-use map[1] corroborates that (US 14%, Canada 12%, UK ~7%), although I do agree that any survey about drug use will probably not see completely truthful answers.
[1]: http://www.theguardian.com/news/datablog/interactive/2012/ju...