Publisher Summary This chapter explains the general system theory that is an organized thought process to be followed in relating cause and effect. General system theory views a system as possessing three basic elements—namely, inputs, transforms, and outputs. A system variable is defined as a quantity or quality associated with the system that may assume any value from a set containing more than one value. Unknown factors can be the witches and goblins of many projects, unknown factors are often uncontrolled, and as a result such systems appear to behave excessively randomly and erratically. In most research and development, the usual approach to identifying the important factors uses a statistical test that is concerned with the risk of stating that an input variable is a factor when, in fact, it is not a risk that is of relatively little consequence.