For our townhouse complex, in a very short time, 60% of the unit were bought up by Boardwalk and rented out to mainly immigrants. I sat on the condo board before, during and after the sale of the units. So I was able to see the changes from the influx of immigrants and it was not good - little boys immediately started trashing anything they could - breaking limbs off the trees, vandalizing the playground, ripping out anything that was planted, like the flower beds leading into all the entrances to the complex. When asked to stop destroying things, the boys told us they didn't have to listen to "women". When we talked to the parents, we were berated for.....I don't even know what, it was just a bunch of screaming and yelling and threatening us.....they were just furious that we had dared to discuss the problem with them. They then informed us that they would sue us if their boys fell from a tree or on the playground and broke an arm or something. End result - the board (I didn't agree with the decision but was out-voted) cut down ALL the trees on the property, removed all the playground equipment and stopped planting anything in the flowerbeds. So yeah - we went from a looking like a nice complex to looking like a 3rd world hellhole within about 3 years. So I left.
I doubt anything like this is included in the "studies" but I imagine we're not the only neighborhood in Canada who has experienced this. So I guess the studies can say one thing, but in real life, I would totally disagree that immigrants reduce crime rates.