Final answer:
The sales director conducted an experiment because they are aiming to establish causality between a treatment applied to sales representatives and its impact on sales performances. Experiments are the most suitable method for this as they can demonstrate a cause-effect relationship through manipulation and control of variables.
Step-by-step explanation:
The sales director conducted an experiment because a treatment was applied to the sales representatives. This is the best design study for the situation because the sales director is trying to establish causality. In an experiment, one group receives the treatment or variable being tested (experimental group), while another does not (control group). The only difference between the two is the experimental manipulation, and therefore, any differences in outcomes can be attributed to that manipulation rather than chance, allowing researchers to establish a cause-effect relationship.
Observational studies and surveys, while useful in establishing correlation, do not manipulate variables and therefore cannot definitively determine causation. Observational studies merely measure characteristics and can record associations between two variables, but without manipulation, it is impossible to rule out other factors that may influence the results. Surveys may collect a large amount of data from a bigger sample, but they rely on self-reported information, which may contain biases.
In summary, when trying to establish causation, particularly in a business setting where one wants to see the effect of a specific treatment or change, an experiment is the most appropriate research method.