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 can only reveal evidence of probable causes; they don`t really offer an explanation. The discovery of causalities is an important step towards understanding the world, but it is only part of what we need. We also need to understand how and why some cases of causation work the way they do. The answers to these questions lead us to the possibility of identifying cause-and-effect relationships. We need to develop theories and hypotheses that underpin the scientific argument.
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. 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. Symbolically, the common method of agreement and difference can be presented as: As an example of the method of difference, consider two similar countries. 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.