Title: The idea of control in experimentation
Course: UGQuants (SSPS) > Section: Causality

The idea of control in experimentation

The key idea behind control is that if we can turn some variables into constants, we can ignore them in our model and concentrate on the behaviour of the variables we are interested in. If we know that some variables are held constant, then we can know for sure that they cannot take part in the causal process we are examining: that is, they will have played no part in any change in value of the dependent variable.

The only sure form of control is the experiment where the value of one or more variables can be manipulated directly. The experience of a control group (where these variables are not been manipulated) can be compared to that of the experimental group. In this manner, the effect of the manipulation of the variable value can be observed directly since any difference between the two groups is almost certainly caused by the manipulation undertaken (providing both groups have been randomly selected so as to neutralize the effect of all other variables). A good example of this would be a clinical trial where one group of patients is given an experimental drug, whilst another group - the control group - is given a placebo.

Such experiments have little use outside laboratories however. Manipulating the values of variables in the real world is often very difficult to do (imagine the cost of an experiment that examined changes in levels of income for example) and is usually ethically problematic. Even where an experimental design is practical and ethical, it faces other problems, such as whether all 'cases' (i.e. people) stay in the study to its completion, or do what they are supposed to (e.g. follow a certain diet, or undertake some other particular form of behaviour). Results may change between the laboratory or other artificial contexts of a controlled study and more real-life settings. Finally, humans in an experiment are almost inevitably aware that they are being studied, and this awareness can alter their behaviour, either consciously or subconsciously.