Documentary research is a scientific method used by many sociologists to gain information from outside sources. External materials such as books, articles, documentary films, and records can be used in a research project to get value and reliable information for the confirmation of a hypothesis. The documentary research is worthy because reduces extra effort made by a group of scientists in finding results on the field. Documentary research is really helpful because the knowledge accumulated by past research can support new inquiries or research problems. All research projects need to make documentary research in order to know the level of academic development in the topic of interest however, it must not be the only scientific method to be used. There is some lack of knowledge that is no possible to reduce by only doing a literature review. It is necessary for social scientists to do some field work. Experimentation, surveys, and ethnographic work are some other scientific methods possible to use in order of reducing edges in knowledge. Field work is also important every research problem has its own peculiarities depending on the social context in which it is created. Social systems are complex furthermore, always is necessary to add other variables wich were not included in previous studies. Understanding domestic violence in Switzerland may not be the same if you try to study the same topic in Congo or China. There might exist a lot of bibliographic literature of domestic violence, however, to understand causes and effects rooted on specific territories it may be needed to make some field work.