Controlled experimentation depends on a reductionist approach which minimizes uncontrolled bias. A small number of factors, say one to four, are chosen as critical to the performance of a task. These factors are varied while all other factors are kept constant, if possible. If varying a factor results in a statistically significant difference in performance, then suggestions for practical implementa- tion can be developed. The factors which the experimenter varies are the independent variables and the performance measures are the dependent varia- bles. The advantage of controlled experimentation is that the results are generaliz- able and replicable. Critics argue that controlled experiments too often have a narrow focus and produce trivial results.