Basics of Research Process

Controlled Experiment Meaning, Importance & Examples in Science

controlled experiment
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A controlled experiment is a research method that tests a hypothesis by manipulating a specific variable, called the independent variable. Researchers keep all other factors constant (controlled) to see how the independent variable affects the outcome, or dependent variable. Control groups are used for comparison, so that any changes can be attributed to the independent variable. A controlled scientific experiment helps establish cause-and-effect relationships and reduces potential bias, leading to more reliable results.

Any study in psychology, sociology, natural sciences and humanities is impossible without conducting experiments. They confirm theories, test new drugs, and develop methods. Besides, students often have to control an experiment while learning.

A controlled scientific experiment — how does it proceed? What determines accuracy and reliability of results? What methods are used by  researchers? We will take a closer look at te definition of a controlled experiement. Read our guide to learn how to rule out mistakes and outside influences in your experiment. You will find many useful suggestions in this article, including tips on how to provide control, exclude an influence of extraneous factors and many more.

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.

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FAQ About Controlled Experiments

1.Why is a control group important in an experiment?

The purpose of a control group in an experiment is to provide a basis for comparing and analyzing effects of an investigated factor on participants in experimental group. It allows you to eliminate an impact of fatal external factors on independent and dependent variables. An experimental group is influenced by an investigated factor. At this time, the control group allows you to assess the progress of the ongoing processes.

2. What is the control in an experiment?

Scientific control in an experiment is necessary to minimize the extraneous variables' influence. It allows you to exclude an impact of an element that is not directly related to essence of a study. It helps focus the attention on the influence of an independent variable. Experimental and control groups comparison prevent errors. It also eliminates observer bias.

3. Why are hypotheses important to controlled experiments?

A controlled experiment's purpose is to confirm or disprove a particular hypothesis. It sets the research direction, allows you to choose methods and highlight important factors. It ensures accuracy of the result, and excludes extraneous influences. The bounded stage allows you to assess the effect of a variable on a control group. Hypotheses are important to experiments as a basis for creating a work plan.

4. What is the difference between a control group and an experimental group?

Experimental group is influenced by an investigated independent variable. This receives the treatment whose effect researchers wish to study. For example, experimenters are testing a new drug’s effectiveness. Whereas a control group does not receive this treatment. Both groups are recruiting volunteers with the same disease. They also should be identical in all other ways. To prevent control group from suffering from a lack of treatment, participants are given previously tested drugs. Experimenters monitor the effects of old and new drugs and compare them.

Article posted on:Sep 26, 2022
Article updated on:May 11, 2023


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