Consider as an example of the two similar countries difference method. Country A has a centre-right government, a uniform system and was a former colony. Country B has a centre-right government, a single system, but has never been a colony. The difference between countries is that Country A easily supports anti-colonial initiatives, while country B does not. The difference method would or would not identify the independent variable as the status of each country as a former colony, the dependent variable supporting anticolonial initiatives. This is because the two similar countries have compared, the difference between the two is whether they were previously a colony or not. This then explains the difference with the values of the dependent variables, the former colony supporting decolonization rather than the country without a history of being a colony. In this case, you are the only one who is not sick. The only difference between you and the others is that you didn`t make a salad. It`s probably the cause of other people`s illnesses. It is an application of the method of difference.
This rule says that if you have a situation that leads to an effect, and another that does not, and the only difference is the presence of only one factor in the first situation, we can infer that factor as the cause of the effect. Mills` methods are five methods of induction described by the philosopher John Stuart Mill in 1843 in his book A System of Logic.  They must shed light on issues of causation. Philosopher John Stuart Mill has developed a series of five methods (or canons) that analyze and interpret our observations in order to draw conclusions about the cause-and-effect relationships they have. 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. As simple as a “common method,” this principle simply poses the application of methods of concordance and difference. “Method of agreement.” Merriam-Webster.com Dictionary, Merriam-Webster, www.merriam-webster.com/dictionary/method%20%20Consecite. Access 30 Nov 2020.
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. Thus, we might find that you felt a little sick after eating an oyster, while your sister was rather comfortable eating a few, and your father became seriously ill after eating ten in a row. Since the variation in the number of oysters corresponds to a variation in the severity of the disease, it would be reasonable to infer that the diseases were caused by oysters. To see how each of the five methods works, we look at their practical application to a particular situation. Suppose an otherwise uneventful afternoon, the university nurse realizes that an unusual number of students suffer from severe digestive disorders.