Has anyone proved that walled homes or residences are more secure?

In most countries, including Rwanda, there are no ugly walls around homes or offices. What we learned from Rwanda about polythene bags should apply to the walls. Curiously, even Kenyan police stations are now surrounded by walls.

Do police feel insecure like the rest of us?  Why are we putting up walls everywhere that seem to be getting higher, topped with either electric or razor wire? The walls are not for keeping off wild animals that are rare in most urban centres except the crow and rats. A few monkeys are found in leafy suburbs.