Experiment!: Planning, Implementing and Interpreting

6.2 Questions, Answers and Experiments

The reason why it is important to distinguish between experimentation and passive observation is that they provide different kinds of evidence. An observational study reveals correlations between variables whereas a well conducted experiment can provide evidence for causation. This is because active and structured manipulation of a system can isolate the effect that one variable has on another. In an observational study we do not take control over the variables, which makes it difficult to work out “what does what to what” in the system.

In Chapter 2 we compared the inductive and hypothetico-deductive approaches to research and concluded that they provide different sorts of knowledge. We said that the inductive approach could only give us descriptive theories, whereas an hypothesis could be a basis for explanatory theory. These two approaches have nothing to do with our definition of experimentation. Both experiments and observational studies can test hypotheses but neither of them has to be hypothesis-driven. If we test hypotheses or not is a matter of how we formulate our research questions.

By contrast, if we experiment or not has to do with how we go about answering the questions. As explained in Figure 6.3, these are two completely independent dimensions of scientific enquiry. The two types of study (observational and experimental) and the two types of research question (non-hypothetical and hypothetical) give us four possible combinations. ...