SPOKANE, Wash.— An insurance study showed states have seen an increase in crashes after legalizing recreational marijuana.

The study was done by The Insurance Institute for Highway Safety (IIHS) and the Highway Loss Data Institute.

Vice President of Highway Loss Data Institute, Matt Moore, told KREM 2 he saw a connection between driving stoned and crashes.

"What we found was that crash risk has increased since the inception of legal retail sales,” said Moore.

Researchers used insurance data to find out how many collision claims were filed in Washington, Colorado and Oregon before and after the law changes.

Researchers also compared the numbers to neighboring states without legalized recreational use.

Critics of the study complained they looked at high density states like Colorado and Washington and compared them to more sparsely populated areas like Idaho. They also complained that it is difficult to prove marijuana caused crashes.