Experimental and Quasi-Experimental Research: Definitions 
Characteristics of Experimental and Quasi-Experimental Research 
Primary Purpose for Experimental and Quasi-Experimental Research  
Research Designs within Experimental and Quasi-Experimental Research

 
Experimental and Quasi-Experimental Research: Definitions 

Dependent variable - the variable that is affected, impacted, changed; it is the "effect" in a cause-and-effect relationship; it is usually identified as Y and is plotted along the vertical axis on a scatterplot 

Independent variable- the variable that is manipulated, the treatment; it is the "cause" in a cause-and-effect relationship; it is usually identified as X and is plotted along the horizontal axis on a scatterplot 

Experimental group - the group of subjects who receive the treatment 

Control group - the group of subjects who do not receive any treatment 

Probability - the expected relative frequency of a particular outcome; the proportion of successful outcomes to all outcomes 

Replication - the reproduction of a research study such that sampling methods, instrumentation, and procedures are the same as a previous study; the sample obtained should be very similar to the previous study 

Bias - personal, unreasoned distortion of judgment 
 

Characteristics of Experimental and Quasi-Experimental Research 

1. Variables are operationally defined by the researcher 

2. Independent variable is directly manipulated 

3. Dependent variable is measured and a cause-and-effect relationship is inferred. 

4. The distinction between the experimental and quasi-experimental is in the random selection and/or assignment of individuals to groups. In a true experimental design, the researcher randomly selects individuals to participate in the study and then randomly assigns those individuals to control/experimental groups. In a quasi-experimental design, the groups (intact classes) may be randomly selected and randomly assigned. Or individuals may be randomly selected but are not randomly assigned. Or individuals may not be randomly selected or randomly assigned. This is due to ethical issues in schools. 

Experimental and quasi-experimental research are conducted for the purpose of establishing evidence related to the cause of a change in behavior / achievement. This design is the only design that can infer cause. The results from an experiment or quasi-experiment should enable the researcher to make cause and effect statements with caveats regarding limitations / generalizability.

Research Designs within Experimental and Quasi-Experimental Research 

1. Single Group - one group is used to measure the impact of the independent variable on the dependent variable; the use of a pre-test and post-test reduces the threats to validity  

2. Experimental and Control Group - one group receives the treatment while the other group receives no treatment; the use of pre-test and post-test reduces the threats to validity; more than two groups can be used, for example, you might want to explore the impact of two new teaching methods, so you could create three groups; one group gets method A, the second group gets method B, and the third group receives the traditional method; the third group functions as the control group 

3. Single Case - one individual is used to measure the impact of the independent variable on the dependent variable usually using a pre-test and post-test (we will discuss this in greater detail when we study Chapter Six of your text). 

  Chapter 3 Experimental and Quasi-experimental Research