Almost everyone I know locks their car doors when they leave their vehicle for an extended time. However, I come from a country town and most people in that country town don't lock their car doors and rarely lock up their houses.
I moved to the city to live when I was 8 years old and have always wondered what the point is in locking your car doors? If someone can start your ignition without a set of keys they can surely, with even less effort, open your car doors.
Is there any evidence to suggest that locking your car door reduces the chance of your car being stolen or reduces the chance of a valuable being stolen from an out-of-sight area (glove box, car boot)?
Examples of the claim that people should lock their doors to prevent vehicle theft: