Some studies have shown that having more police present increases crime, but some say it reduces it. A study by Jonathan Klick showed that having a higher police presence can cause a major reduction in crime. That being said, it would be very costly to have a police presence on every block, so towns faced with crime could look into other means to deter it as well, such as surveillance cameras.
The term used is omni presence. If a would be crook has just seen a police vehicle cruise by; he or she will naturally think twice about committing a crime. You never know when that cruiser or another one might come back by. Also, a witness to an incident can be assured police are in the area and can respond quickly. As a retired cop I speak from experience and caught many a criminal by just being at the right place at the right time. Now with budget cuts and lay offs, I talk to people all the time who complain about slow response these days and some departments won't even respond to accidents without injuries anymore.
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