Perhaps the best way to introduce Mills` methods is an example. Suppose your family went to a buffet dinner together, but when you got home, you started to feel sick and feel stomach pains. How do you determine the cause of the disease? Suppose you create a table of foods that are taken by each member of the family: Precise determination of causes and effects is not an easy task. We can often confuse or misrepreseg the two because we lack sufficient information. Mill`s methods are attempts to isolate a cause from a complex sequence of events. The common method deals with both the method of agreement and the method of difference as indicated by the diagram above. The application of the common method should therefore tell us that this time it is beef that is the cause. Unlike the four previous inductive methods, the method of accompanying variation does not involve the elimination of any circumstances. The change in size of one factor causes another factor to change in size. Mills methods should not come as a surprise, as these rules articulate some of the principles we use implicitly in causal reasoning in everyday life.
But it is important to respect the limits of these rules. So far, I have talked a lot about observations and how we can improve them, but we often observe to learn more about causal relationships, what depends on what? I will conclude our discussion of observations by introducing a framework that we can use to understand how scientists draw conclusions based on their observations, experiences and simulations. The logic of observation is based on conclusions was described by John Stuart Mill, a philosopher best known for writing about freedom, but who also has many contributions on how we think about science. Mill was interested in how we can use observations and experiences to determine the causes or what depends on them. He introduced a series of methods to reflect on the empirical data that we now call Mills` methods. I will talk about the first two of his methods; what we now call the method of agreement and the method of disagreement. So, to think about these methods, let`s make a distinction between the results and the conditions. Let`s say there was an outbreak of food poisoning at a local restaurant. The fact that people have fallen ill is the result. The various foods that people were doing, the different restaurants where they were, and people`s health stories are the conditions.
Scientists have often cited the results of dependent variables and the different conditions of independent variables. I use those terms. Mill`s method of agreement is therefore simple.