It presents a system of classification for research methods. Authors must use this system in manuscripts submitted to the International Journal of Clinical and Health Psychology.

It describes the different types of research methods in the field of psychology in a functional and user-friendly way for authors. This means that the system we have elaborated is clear, valid and operative, creating a standard code which facilitates communication among authors. It is also useful for doing "second-order" research, such as meta-analytical or bibliometrical studies. In addition, it is a good tool for selecting the most accurate research design for a given investigational problem.

It provides a common language among researchers and facilitates reflection on research quality.

We were interested in describing the amount of use of different types of research methodologies among researchers in the field of psychology within our country, Spain. For doing so, we previously had to elaborate on a classification system for those types of methodologies. That study (Montero & León, 2001) was selected by the National Psychological Association (COP) to be included (and translated into English) in an electronic journal, entitled "Psychology in Spain" (Montero & León, 2002a).

It gave our work a better salience among our colleagues, so, the editors of the International Journal of Clinical and Health Psychology contacted us, asking for a paper in which we would present, justify, and detail our system of classification for research methods.

Their idea was to transform our proposal into the system for the Journal. We accepted the task and published a first version (Montero & León, 2002b). Last year we published a second version in the same Journal, increasing the quality of this system of classification with the experience we had gained during these intervening years (Montero & León, 2005).