Section 1-4

Observational and Experimental Studies

Objective 6: Explain the Difference Between and Observational and Experimental Study

In an observational study, the researcher merely observes what is happening or what has happened in the past and tries to draw conclusions based on these observations.

In an experimental study, the researcher manipulates one of the variables to determine how the manipulation influences other variable.

Variables

1. Independent or Explanatory variable

2. Dependent or outcome variableThe researcher manipulates the independent (explanatory) variable and tries to determine how the manipulation influences the dependent (outcome) variable in an experimental study.

VariablesConfounding variableA confounding variable influences the dependent variable but cannot be separated from the independent variable.

For example, you want to study whether bottle-feeding (Cause) is related to an increased risk of diarrhea in infants (Effect). It would seem logical that bottle-fed infants are more prone to diarrhea since water and the bottle could get contaminated, milk could go bad, etc. But if you were to conduct this study, you would learn that bottle-fed infants are less likely to develop diarrhea than breast-fed infants. It would seem that bottle-feeding actually protected against the illness. But in truth, you would have missed a very important confounding variable - mother's education.

If you take mother's education into account, you would learn that better-educated mothers are more likely to bottle-feed their infants, who are also less likely to develop diarrhea due to better hygienic practices of the mothers. In other words, mother's education is related to both the Cause and the Effect. Not only did the Confounding Variable suppress the effect of bottle-feeding, it even appeared to reverse it - confounding results, indeed!

1-4 Observational and Experimental Studies

6Bluman Chapter 1

On your own

Read sec 1.4 Applying concepts 1-4 on page 16

Problems 17, 18 on page 27

Bluman Chapter 1 7