Experimenting   

The process of determining the effects of one or more variables
in order to test the validity of a hypothesis.

1. The experimenter manipulates one variable to determine its effect on the other.
2. In experiments, the variable that is manipulated by the researcher  is called the "Independent Variable".
3. The other variable is called the "Dependent Variable" because its value is presumed to be dependent upon the "Independent Variable".
4. Manipulation of an independent variable means that the researcher produces differences in the indpendent variable that did not exist before the study.

1. No independent variable is manipulated by the researcher.
2. The researcher selects a sample to study. Samples are selected from each of the populations to be compared. For example, rates of tuberculosis infection might be compared for populations of people living in poverty and those with middle class incomes.
3. The researcher then takes measurements of the variable that is of interest and compares differences between the groups.