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Descriptive, or qualitative, methods include the case study, naturalistic observation, surveys, archival research, longitudinal research, and cross-sectional research. Experiments are conducted in order to determine cause-and-effect relationships.
A controlled experiment is the only research method that can establish a cause and effect relationship. An effective way to determine the independent and dependent variables is to word the hypothesis in the form of an “If …, then …” statement.
True experiments have four elements: manipulation, control , random assignment, and random selection. The most important of these elements are manipulation and control. Manipulation means that something is purposefully changed by the researcher in the environment.
While there are several important considerations that go into creating a good experiment, the essential parts are the treatment and the control. The experimental treatment is the thing that you are testing.
Experimental studies are ones where researchers introduce an intervention and study the effects. Experimental studies are usually randomized, meaning the subjects are grouped by chance. The researchers then study what happens to people in each group. Any difference in outcomes can then be linked to the intervention.
The most popular ones are completely randomized design, randomized block design, Latin square design and balanced incomplete block design. In this chapter, we will discuss these four designs along with the statistical analysis of the data obtained by following such designs of experiments.
Single Factor design. • An experiment concerns with 1 independent variable (factor), and N levels. • Abuse of language: “condition” is used as factor and levels.
A two-factor factorial design is an experimental design in which data is collected for all possible combinations of the levels of the two factors of interest. The design size is N = abn. • The effect of a factor is defined to be the average change in the response associated with a change in the level of the factor.
A factor of an experiment is a controlled independent variable; a variable whose levels are set by the experimenter. A factor is a general type or category of treatments. Different treatments constitute different levels of a factor.