There are many different types of “experiments.” Most are quite different from the common stereotype. All experimental research, however, has several elements in common. One of the most obvious is the division of the subjects into groups (control, experimental, etc.). Another is the use of a “treatment” (usually the independent variable) which is introduced into the research context or manipulated by the researcher. The four research parameters will help us understand the other distinguishing characteristics of experimental research.
The study might include an intervention such as a training programme, some kind of social activity, the introduction of a change in the person’s living environment (e.g. different lighting, background noise, different care routine) or different forms of interaction (e.g. linked to physical contact, conversation, eye contact, interaction time etc.). Often the interaction will be followed by some kind of test (as mentioned above), sometimes before and after the intervention. In other cases, the person may be asked to complete a questionnaire (e.g. about his/her feelings, level of satisfaction or general well-being).
Some studies are just based on one group (within-group design). The researchers might be interested in observing people’s reactions or behaviour before and after a certain intervention (e.g. a training programme). However, in most cases, there are at least two groups (a between-subjects design). One of the groups serves as a control group and is not exposed to the intervention. This is quite similar to the procedure in clinical trials whereby one group does not receive the experimental drug. This enables researchers to compare the two groups and determine the impact of the intervention. Alternatively, the two groups might differ in some important way (e.g. gender, severity of dementia, living at home or in residential care, etc.) and it is that difference that is of interest to the researchers.
KINDS OF EXPERIMENTAL RESEARCH
Within the realm of experimental research, there are three major types of design:
If you choose to conduct experimental research, one of your most important tasks will be to choose the design that gives your research the best combination of internal and external validity. At the same time, it must be practical enough so that you can actually do the research in your own circumstances.
Remember, no particular type is right for all situations. Real-world constraints will often dictate what is practical or possible. In any case you need to be careful to recognize the weaknesses of the design you choose. Do not attempt to prove things or make claims in your findings that are beyond the capabilities of your design.
TRUE-EXPERIMENTAL DESIGNS must employ the following:
- Random selection of subjects
- Use of control groups
- Random assignments to control and experimental groups
- Random assignment of groups to control and experimental conditions
In order for an experiment to follow a true-experimental design, it must meet the preceding criteria. There is some variation in true-experimental designs, but that variation comes in the time(s) that the treatment is given to the experimental group, or in the observation or measurement (pre-test, post-test, mid-test) area.
To understand the nature of the experiment, we must first define a few terms:
- Experimental or treatment group – this is the group that receives the experimental treatment, manipulation, or is different from the control group on the variable under study.
- Control group – this group is used to produce comparisons. The treatment of interest is deliberately withheld or manipulated to provide a baseline performance with which to compare the experimental or treatment group’s performance.
- Independent variable – this is the variable that the experimenter manipulates in a study. It can be any aspect of the environment that is empirically investigated for the purpose of examining its influence on the dependent variable.
- Dependent variable – the variable that is measured in a study. The experimenter does not control this variable.
- Random assignment – in a study, each subject has an equal probability of being selected for either the treatment or control group.
- Double blind – neither the subject nor the experimenter knows whether the subject is in the treatment of the control condition.
Advantages of the true-experimental design include:
- Greater internal validity
- Causal claims can be investigated
- Less external validity (not like real world conditions)
- Not very practical
QUASI-EXPERIMENTAL DESIGNS are usually constructions that already exist in the real world. Those designs that fall into the quasi-experimental category fall short in some way of the criteria for the true experimental group. A quasi-experimental design will have some sort of control and experimental group, but these groups probably weren’t randomly selected. Random selection is usally where true-experimental and quasi-experimental designs differ.
Some advantages of the quasi-experimental design include:
- Greater external validity (more like real world conditions)
- Much more feasible given time and logistical constraints
- Not as many variables controlled (less causal claims)
PRE-EXPERIMENTAL DESIGNS are lacking in several areas of the true-experimental criteria. Not only do they lack random selection in most cases, but they usually just employ a single group. This group receives the “treatment,” there is no control group. Pilot studies, one-shot case studies, and most research using only one group, fall into this category.
The advantages are:
- Very practical
- Set the stage for further research
- Lower validity