There are a number of variations on the basic model shown here which include two or more experimental groups and the control group or alternative treatment groups. True experimental research can claim high internal validity because of the control imposed on all intervening variables; this could be interpreted as high integrity of findings if there is sufficient evidence that intervening variables have in fact been controlled. This research design is the most suitable for testing hypotheses which involve causal relationships, but be sure you have read and understood the section on causality before you attempt to demonstrate it using this approach. Experiments are a very expensive form of research in terms of facilities needed. A laboratory is a major resource as is the time of the research participants, and they are dependent on strict control features, which are not always possible.