Under a landmark federal law enacted in 1968, a (an) may be defined as an act of violence by one or more persons part of an assemblage of three or more persons that results in property damage or personal injury.

answer:

d. because dr. laguardia selected a widely used measure, his study generalizes to has strong external validity. external validity has limited external validity. other applications of this measure.

the widely used measure that he applied to his experiment was the benton facial recognition test. it employed on to football players and as result, only players who suffered brain concussions did not pas this test. and although it has an external validity, it is limited because it isn't general to apply to other population.