08 March 2013

Is it an experiment?

“Is this a study, or is this an experiment?”

I ask students this question a lot, both undergraduates and master’s, and they struggle to find an answer. This surprises me, given that experimental evidence is arguably the gold standard for scientific evidence. That is not to say experiments are the only scientific evidence; there are many fields of completely respectable science where you can’t do experiments easily.

The difference between an experiment and a study is manipulation. That is, did the scientist actively change something, or just collect data from the world as it is?

For instance, sampling DNA from fifty species of fish to determine the relationships between them is a study, not an experiment. Observing a hundred thousand galaxies to see how many are red shifted is not an experiment. Searching for a predicted transitional fossil in geographic starta of a certain age is not an experiment. Those are all studies, not experiments.

If a human being actively intervenes in a system somehow, then you have the potential for an experiment. Adding a chemical to a mixture, removing a nutrient from a diet, showing pictures to an undergraduate, or changing how you word a survey question are all experimental conditions.

An experiment does not necessarily mean you have a control group. You can have an uncontrolled experiment. That’s not ideal, but it still qualifies as an experiment.

You can also have a natural experiment, where there has been a intervention, but not by people. The qualifier is important there, as it points out that a natural experiment is something slightly, but importantly, different from a normal experiment.

The difference between an experiment and a study should be as important a distinction to as the difference an hypothesis and a theory.

Photo by jimmiehomeschoolmomon on Flickr; used under a Creative Commons license.

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