Political parties are to express the wishes of the people.

I believe the answer is: Instruments

The role as instruments mean that political party could be used as some sort of tools that the people use to get their aspiration across the government body. This is why politicians are considered to be 'public servants', because they inherently exist to fulfil the will of the people.

disorders of the brain include both behavior disorders and other psychiatric illnesses. the primary difference between a behavior disorder and another type of psychiatric disorder is the presence of choice. psychiatric conditions are considered to be involuntary while in behavior disorders, choices are essential.

answer; a cost benefit analysis;