A quarter of robberies of commercial premises in the U.S. are committed with guns.[152] Fatalities are three times as likely in robberies committed with guns than where other, or no, weapons are used,[152][153][154] with similar patterns in cases of family violence.[155] Criminologist Philip J. Cook hypothesized that if guns were less available, criminals might commit the same crime, but with less-lethal weapons.[156] He finds that the level of gun ownership in the 50 largest U.S. cities correlates with the rate of robberies committed with guns, but not with overall robbery rates.[157][158] He also finds that robberies in which the assailant uses a gun are more likely to result in the death of the victim, but less likely to result in injury to the victim.[159] A significant number of homicides are the consequence of an unintended escalation of another crime in which firearms are present, with no initial intent to kill.[154][160] Overall robbery and assault rates in the U.S. are comparable to those in other developed countries, such as Australia and Finland, with much lower levels of gun ownership.[156][160] A strong association exists between the availability of illegal guns and violent crime rates, but not between legal gun availability and violent crime rates.[161]