Reply #33: It's done all the time in every scientific discipline [View All]

[Time for change]

It's referred to as using a control group.

For example, it was established several years ago that that aspirin is a cause of Reyes syndrome (a fatal liver disease) in children who take aspirin when they have influenza. The only way to assess this was to compare the incidence of Reyes syndrome in children with influenza who took aspirin during their illness with those who didn't.

Or, sometimes it works the other way around, and it's found that people who lack certain exposures are at higher risk for certain diseases. For example, children who are NOT exposed to fluoride in their water supply are at much higher risk than children who drink fluoridated water to develop dental carries.

It's more complicated than that, because there are several criteria for assessing a causal realtionship between two variables once a correlation has been established. But the point I'm trying to make here is that virtually all scientific studies make use of a control group (i.e., unexposed) to compare with an exposed group, in order to ascertain the difference between them.

Does that answer your question, or would you like me to describe the criteria that are used to establish a causal relationship once a correlation has been established?