On the basis of the nature of the investigation, the study designs can be classified into three types of studies:
- Experimental study design
- Non-experimental study design
- Semi-experimental or quasi-design
The experimental study design
The experimental study design is one of the most commonly used study design in the social science, psychology, marketing, business, and education. There are many types of experimental study designs that are used in the research. A true experimental design has the greatest internal validity as compared to any other design. Experimental design is the best one to use when the researcher wants to establish the cause and effect relationship. Other types of designs might prove to be weak when the researcher wants to establish causal relationships. An experimental study design can be one of the following types:
- Before and after experimental design
- After only experimental design
- Random or control experimental design
- Comparative experimental design
- Placebo experimental design
These designs and several other types of experimental design have further sub-types like a placebo design can be a simple placebo design or a control placebo design. A control experimental design can be a simple control design or a double control design. Every design in the experimental study design has sub-categories. Therefore the application of the experimental designs is for a wider range of research topics and subject areas.
Before and after experimental design
In a conventional before-and-after study design, the researcher investigates or observes the audience before the intervention is introduced to them. The other observation is taken after the intervention has its effects on the audience. This experiment can compare the change that has taken place due to the introduction of the intervention to the audience.
After only experimental design
The after-only design is a really simple design and it takes less time and energy to conduct it. The researcher does not compare the before observation with the after observation. The researcher does not take first-hand information for the before the introduction of the intervention. He relies on the available records or memory recall of the audience. The after effects of the intervention are observed and the researcher draws the conclusion about how effective the intervention is for the audience.
Random or control experiment
This is a very useful design as far as the validity is concerned. The investigator takes two groups; one group is a control group and the other group is the experimental group. The control group does not receive any treatment or intervention. The experimental group receives the treatment. The investigator takes before the observation of the both groups and then after the intervention is introduced he takes another observation. The difference between both observations is attributed to the effect of the intervention.
Comparative experimental design
In an experimental comparative design, the investigator wants to establish differences in the effectiveness of different treatments. He assigns different groups and takes baseline measurements or observation of each group. After the baseline observations he introduces different treatments to each group and after he is sure that the treatment has its effects he takes another measurement or observation of each group. A comparison is made between the results of each group and in this way he can establish which treatment is more effective and which one is not.
A placebo experimental design studies the psychological and medicinal impacts of the treatment on the audience. The investigator takes several groups and he introduces treatment to one group and to the other group, he just gives an inert treatment. The purpose is to know the psychological impact of getting treatment for the patients. In other situations when a new medicine has introduced the pharmacist conducts a placebo study to know the effectiveness of the medicine on the patients.
Non-experimental study design
The aim of the non-experimental study design is to collect one time information. This information can be collected using any first hand or second hand evidences. Most of the time such studies are descriptive in nature.