A manager invited me to try and test the physical security of his office door lock (by non-destructive means, i.e. not ramming the door down). I found that since the door opened from inside by a handle (which automatically unlocked the lock -- i.e. even if the door was locked, all you had to do was push the handle down from the inside to open it), and since there was a 1/2-inch gap between the bottom of the door and the floor, you could open the door by sliding a coat hanger under the door, rotating the coat hanger in order to loop a piece of wire over the door handle, and then pulling the wire from under the door in order to pull the handle downward.
OK. But I've never seen any guidelines for physical security which explicitly say that doorknobs are more secure than door handles. A Google search for "doorknobs vs door handles security" turns up nothing useful.
Have you ever seen a list of guidelines for physical security that recommends doorknobs over door handles? It seems like something that would significantly increase physical security of locked doors no cost. If a list of guidelines doesn't include this, I would consider it incomplete.
(Obviously neither does much good against a smash-and-grab attack, but the coat hanger would be useful in situations such as (a) nobody's watching you, but there are other people on the same floor who would hear you if you smash the door open, or (b) you want to avoid the break-in being detected after the fact.)