The aim of the experimental research is to investigate the possible the “cause-effect” relationship by manipulating one independent variable to influence the other variables in the research problem and by controlling the other variables and by measuring the effects of the manipulation by other means. By changing the independent variable, the researcher can see if the treatment makes any difference on the subjects.
There are two purposes of doing experimental research:
(i) To provide answers to research questions.
(ii) To control variance or differences.
If the average scores of two groups prove to be significantly different and if there are not any explanations for these differences, then we can conclude that the effect of the treatment caused these differences. Thus, experimental research may differ from correlation research. There are some independent variables such as age and gender that cannot be altered. When the independent variable chosen, cannot be manipulated either a comparative research is conducted or another independent variable is chosen for manipulation in order to conduct an experimental study.
The main function of the experimental research design is to control variance by maximizing systematic variance, controlling extraneous systematic variance and minimizing error variance.
Therefore the researcher attempts to:
- Maximize the variance of the variables of the research hypothesis i.e. maximize the difference in the dependent variable caused by maximizing the differences in the independent variable.
- Control the variance of extraneous or “unwanted” variables that may have an effect on the experimental outcomes but which he/she is not interested.
- Minimize the error or random variance i.e. avoid unreliable measurement instruments which have high errors of measurement.
We can maximize experimental variance by designing, planning and conducting research in such a way that experimental conditions are as different as possible on the independent variable.
Control of Extraneous variables:
- Eliminate the variable viz. if you are worried about gender, only include one gender in the study.
- Randomization viz. if you randomly assign subjects to groups, the extraneous variable should be equally distributed among the groups.
- Build it into the design viz. if you are worried about gender, build it into the analysis. (e.g. by 2-way ANOVA)
- Match subjectsi.e. match the characteristics of subjects and put one of each matched pair in each group.
Minimizing Error Variance: It has two principle aspects:
- Reduction of errors of measurement through controlled conditions i.e. standardize testing procedures
- Increase in the reliability of measures i.e. revise test instruments or find more reliable ones.
Different types of experimental research can be conducted depending on the subjects and the instruments and the way data are collected and analyzed.
Answers to the following questions would determine what type of experimental design is to be followed:
(I) Whether there is a need for a control group?
(II) How many subjects are required?
(III) Are subjects to be selected randomly?
(IV) How will the obtained data be analyzed?
(V) What are the factors that may affect the internal validity?
(VI) What are the factors that may affect the external validity?