Epidemiological studies have indicated that antisocial personality disorder is one of the most common personality disorders, with approximately percent of the general population being diagnosed with the disorder at some time in their lives.

4 percent                                                

Explanation:

Epidemiological studies are described as studies that are being related to the disease or disorder in human and animal populations, significantly where, how, and when they occur.

An antisocial personality disorder is described as one of the mental conditions whereby an individual encompasses a "long-term pattern" of violating, manipulating, and exploiting someone else's rights in the absence of any regret or remorse.

In the question above, the given statement signifies "four percent".

b) to encourage free trade

answer; fair labor and standard act;