Controlled Experiment Meaning, Importance & Examples in Science

What Is a Controlled Experiment: Definition

A controlled experiment is testing under programmed conditions. It’s the main tool for testing advanced scientific theories. Validity and effectiveness of scientific research depend on the experiment’s accuracy. This method is actively used in medicine. It is also used in social and natural sciences, psychology, and biochemistry.

There are two main parts of such an experiment:

• test factor
• experimental and control groups.

External influences on both groups must remain constant. Experimental group help researchers test substances or effects. Control group is not affected by this effect. Experimenter observes an influence of independent variables on dependent variables. Excluding extraneous influences ensures that you receive statistically valid results.

Importance of Control in an Experiment

Extraneous variables should not affect the course of an experiment. The role of a control in an experiment is to exclude external factors and ensure high internal validity of results.

The main purpose is to eliminate outside influences. And also you should be able to maximally manage an effect of an independent variable. That makes it possible to exclude mistaken hypotheses about an observed effect.

At the same time, it is necessary to ensure high internal validity. It means measuring the exact impact of an independent variable on a dependent one. External validity is an ability to transfer test results outside the research framework.

Before doing such kind of an experiment, find out the difference between reliability and validity beforehand.

Examples of Controlled Experiments

Several interrelated variables can be examined in a single study. Controlled experiments explore relationships between people. They also explore altered states of consciousness or medication effects. Distribution of participants should be made randomly. It should be done to exclude an influence of external factors. Consider controlled experiment example in somnology.

For example, the effect of sleep duration on concentration is being investigated. A study may include assessing different sleep duration effects. Dependent variable is an ability to concentrate as measured by cognitive tests results. Independent variable is sleep duration. Statistical measurement methods will determine changes in concentration of a person's attention depending on a sleep duration. So what is controlled in this experiment? Any external factors that may distort the relationship between independent and dependent variables.

Methods Used in Controlled Experiments

Choosing methods depends on controlled experiment conditions. Besides, a research on new medications is being conducted on volunteers. Consider these methods of forming samples of groups:

• Parallel Each object of research is assigned randomly. Everyone is influenced by factor being investigated.
• Crossover Each participant is influenced by independent variable in a random sequence.
• Cluster Previously established groups of objects are investigated.
• Factorial Distribution of objects influenced in group occurs randomly.

A laboratory test provides maximum experimental control. It allows you to standardize sampling conditions and reproduce identical conditions for subsequent experiments.

Randomized Controlled Experiment

It is necessary to see the difference between controlled experiments and quasi-experiments. The latter does not give a real picture of the phenomenon under study. Random assignments ensure that an experimental study is objective.

Each subject receives an equal opportunity for experiment. Random selection allows you to compose a large population of participants in an experiment. 

If principles of random distribution are violated, then we have quasi experiment. Its results can be predicted in advance and they are not reliable.

Control Group in an Experiment

Scientific research suggests the need to compare tests and experiments results with behavior of a control group. This is especially important when you conduct medical test on effects of treatments and new drugs.

Comparison of control and experimental groups’ well-being allows one to draw conclusions about taking some drug. In the control group, changes may also occur against the background of taking a placebo. Precise monitoring is essential to distinguish treatment outcomes from psychological factors.

Blinding in an Experiment

In medicine, the most reliable method is double-blind placebo-controlled experiment. When conducting it, not only participants, but also researchers do not know about distribution into groups. This ensures that all participants in experiment behave naturally. They eliminate bias. 

Experimental group gets test drug during course of the study. If patients cannot do without treatment, they are given a drug of proven action. Control group gets a placebo, masking some real medicine.

Pros and Cons of a Controlled Experiment

The advantage of controlled experiment is:

• Demonstrable cause-and-effect relationship between an investigated factor and its influence on experimental group;
• Possibility to exclude external variables;
• Impact of the researcher’s bias is ruled out;
• Ability to study random groups of participants;
• Test results can be verified;
• Data can be combined with results from other studies.

These advantages are necessary to ensure an external validity of results.

The disadvantages are:

• Attempts to manage numerous variables is time-consuming and requires many precise data;
• There are huge numbers of variables and managing all variables is almost impossible;
• Researcher’s personal bias may intrude;
• Groups may not be comparable;
• Human response can be difficult to measure;
• Results may only apply to one situation and may be difficult to replicate.

Such tests have their disadvantages, so scientists and researchers should find a balance between the benefits it provides and the drawbacks it presents.

Bottom Line

Summing up, it is necessary to emphasize the relevance of control science experiments. Not all companies, nor all private researchers have opportunity to organize a large-scale experiment. 

The theory confirmation in psychology, sociology, medicine, biochemistry is impossible without experimental research. Among these, it is the most reliable method for predicting possible outcomes. The experimental techniques limit the influence of extraneous effects. They also limit an observer's intervention during a test.