The primary difference between true experiments and quasi experiments is that quasi experiments do not use random assignment into treatment or control groups since this design is used in existing naturally occurring settings.

Groups are given pretests, then one group is given a treatment and then both groups are given a post-test. This creates a continuous question of internal and external validity, since the subjects are self-selected. The steps used in a quasi design are the same as true designs.

Ex Post Facto Designs

An ex post facto design will determine which variables discriminate between subject groups.
Ex post facto studies cannot prove causation, but may provide insight into understanding of phenomenon.

Focus Groups

A focus group can be defined as a carefully planned discussion designed to obtain perceptions on a defined area of interest in a permissive, nonthreatening environment.

Data mining
Secondary data collected primarily for some other purpose provides a framework for the research project, development of research question(s), and validation of study findings. 

Content Analysis
Content analysis systematically describes the form or content of written and/or spoken material. It is used to quantitatively studying mass media. The technique uses secondary data and is considered unobtrusive research.

Meta-analysis combines the results of studies being reviewed. It utilizes statistical techniques to estimate the strength of a given set of findings across many different studies.

Multimethod Approach
The multimethod approach encourages collecting, analyzing and integrating data from several sources and the use of a variety of different types of research methods.