What is the approach used by psychologists and other scientists to systematically acquire knowledge and understanding about behavior and other phenomena of interest called?

The scientific method.

Physiologists, and other social scientists, use poor methodology and their disciplines are incoherent. About two years ago Nature published a study that addressed the issue of why scientists do not work with social scientists and if they once did once work with social scientists why they no longer do. Methodological sloppiness was the number one problem sited with the work of social scientist.

PS: Next time excise the question numbers and it won't be as obvious that you are trying to get someone to do all your homework.