This is the 2007 version. Click here for the 2017 chapter 01 table of contents.

Experimental Research and its Pitfalls

So far we have concentrated on observational research, giving special attention to problems with questionnaires, because questionnaires are so common and undergraduates are often asked to conduct questionnaire research. Now we turn to the experimental research.

Experimental research is defined by the presence of a manipulation. A manipulation is a change that a researcher deliberately produces in a system. This conforms to the common-language meaning of experiment , which is "to make a change and see what happens." Experimental research is sometimes called manipulational research.

What defines experimental research? What is its "special strength"?

The special strength of experimental research is that it can be used to test cause-effect claims Cause-effect claims are those that assert, "A makes B happen" or "A brings about B." The implication is that if you want to change B, you can do it by changing A. The only ways to gather evidence for or against such a claim is to do an experiment, in other words, change A to see if B changes.

Most of our examples will come from psychology, of course. However, in any field of study, cause-effect claims are some of the most important and hotly debated. Here are some examples of cause-effect claims in different areas.

Law : "Mandatory minimum sentencing would lower the crime rate" I.e. mandatory minimum sentencing would cause a reduction in crime. Or: "The death penalty doesn't work." I.e. the death penalty does not cause a reduction in violent crime.

Medicine : "Passive inhalation of tobacco smoke can increase risk of lung cancer." I.e. inhaling somebody else's smoke causes lung cancers in some people. Or: "Alcohol consumed during pregnancy can harm the fetus." I.e. alcohol can cause disorders in the unborn baby.

Athletics : "Visualizing yourself making a great performance will increase your chances of making a great performance." I.e. visualization causes great plays. Or: "Teams with better physical conditioning do better toward the end of a contest." I.e. good conditioning causes better endurance.

Economics : "Deficit spending increases inflation." (i.e. causes prices to go up). Or: "Productivity is increased when taxes are cut" (i.e. cutting taxes causes more productivity).

Nutrition : "Saturated fats cause heart disease." Or: "Eating eggs causes increased cholesterol levels."

Why are cause-effect claims so hotly debated? How can such claims be tested?

The reason cause-effect claims are so hotly debated is that they have implications for policy. If the death penalty does not work, why have one? If passive inhalation of smoke causes cancer, should public smoking be allowed? Cause-effect claims raise vital economic and political questions. They influence our decisions on matters ranging from law making to personal health.

The only way to test a cause-effect claim is to manipulate the suspected cause and measure the suspected effects. Like observational research, it sounds simple. But, as with observational research, there are many pitfalls or ways to make mistakes.

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