Correlations Explained in a Simple Way
This video screen cast provides with the simple guideline about analyzing correlations. There are three examples such as correlation between ice cream andcriminal rate during summer. Shoe size and reading ability. Smoking and lung cancer.
Ice Cream and Criminal Rate During Summer
In a certain city, research exhibited a strong, positive relationship between ice cream sales and crime. When sales went up, consequently did crime and vice versa. Does this mean that buying ice cream causes crime? Or is there some extra factor involved, such as meteorological conditions or time? People buy more ice cream in warmer months. People are also outside more in warmer months with their homes unattended for longer periods of time. If you incorrectly assume that ice cream causes crime, would you stop the sale of ice cream in order to combat crime? As a result of additional variables and incomplete context, it is hard to justify a causal relationship between ice cream and crime.
Shoe Size and Reading Ability
Consider elementary school students' shoe sizes and scores on a standard reading exam. They are correlated, but assert that larger shoe size causes higher reading scores is as ridiculous as saying that high reading scores cause larger shoe size. In this example, there is a clear hidden variable, namely, age. As the child gets older, both their shoe size and reading ability increase.
Smoking and Lung Cancer
We know that smoking causes cancer. But we also know that many people who smoke don’t get cancer. And people who don't smoke, they also get cancer. Causal claims are not falsified by counterexamples. Let's consider the relationship between cigarette smoking and lung cancer. In 1964 the United States’ Surgeon General issued a report claiming that cigarette smoking causes lung cancer. Unfortunately, according to Pearl the evidence in the report was based primarily on correlations between cigarette smoking and lung cancer. As a result the report came under attack not just by tobacco companies, but also by some of the world’s most prominent statisticians, including the great Ronald Fisher. They claimed that there could be a hidden factor – maybe some kind of genetic factor – which caused both lung cancer and people to want to smoke (i.e., nicotine craving). If that was true, then while smoking and lung cancer would be correlated, the decision to smoke or not smoke would have no impact on whether you got lung cancer
Guideline Approach With Common Sense to Annalyze Correlations
- Find additional information about topic and given variables
- Find hidden variables
- Determine if hidden variable has any relationship with given variable
- Correlation is causation or correlation is causation
Other Examples on Correlation and Causation
This presentation provides other examples on correlation and causation in graphical form