The strategy of placing metal detectors at airports and increasing screening of passengers before they board planes has elements of situational crime prevention as well as those of deterrence and rational choice theory. Situational crime prevention focuses on reducing the opportunities for crime, while also increasing an offender’s perceived risk of apprehension. This can include efforts such as target hardening. Generally, the purpose of target hardening is to make physical entry more difficult or more risky.
Deterrence and rational choice theory holds that humans are rational beings who consider the consequences of their actions and are deterred from engaging in continual patterns of offending as a result of the certainty, severity, and celerity of punishment. It assumes that individuals weigh the costs and benefits of crime, and therefore crime can be prevented by increasing the costs or decreasing the rewards of committing a crime. Counterterrorism strategies, such as the use of metal detectors, attempt to raise the perceived cost of committing terrorist acts, such as hijacking, by increasing the certainty of detection.
So, unless you somehow know exactly how many terrorist were or were not deterred by such actions, any statistics that you might throw out there are meaningless.