What are the major types of unobtrusive methods? Give an example of each from studies in criminology and criminal justice.

What are the major types of unobtrusive methods? Give an example of each from studies in criminology and criminal justice.
What are the relative advantages and disadvantages of unobtrusive measures as a strategy of research?
Be sure to include a title page, one to two pages for the body of your paper, and a reference page. At least two outside references (other than the textbook) are required.