Controlled experiments: methods, examples and limitations (2023)

What happens in experimental research is that the researcher manipulates the independent variables to determine their effects on the dependent variables.

Therefore, if the experiment is controlled, you can expect the researcher to control all other variables except thatindependent variables. This is done so that the other variables do not affect the dependent variables.

In this article we will look at a controlled experiment, how important it is in a study and how it can be designed. But before we dig deep, let's take a look at the definition of a controlled experiment.

What is a controlled experiment?

In a scientific experiment, a controlled experiment is a test that is modified directly by the researcher to test only one variable at a time. The only variable examined is then the independent variable.

This independent variable is manipulated by the researcher in such a way that its effect on theHypothesis or data studiedis known. While the researcher studies the single independent variable, the controlled variables are held constant to reduce or offset their impact on the research.

To achieve a controlled experiment, theresearch populationis usually divided into two groups. Then the treatment is administered to one of the two groups while the other group receives the control conditions. This other group is called the control group.

Controlled experiments: methods, examples and limitations (1)

The control group receives the standard conditions and is placed in the standard environment and also allows comparison with the other group called the experimental group or treatment group. Determining the difference between the behavior of these two groups is important because in any scientific experiment, demonstrating the statistical significance of the results is the only criterion for accepting the results.

So, to determine whether the experiment supports the hypothesis or whether the data is a result of chance, the researcher looks at the difference between the control group and the experimental group. Then the results from the differences are compared to the expected difference.

For example, one researcher wants to answer this question: do dogs have a taste for music too? In case you're wondering, yes, there are studies by researchers on how dogs respond to different genres of music.

Going back to the example: The researcher can develop a controlledExperimentwith high regard for the variables that affect each dog. Some of these variables that can affect the dog are: the dog's environment when listening to music, the temperature of the environment, the volume of the music, and the presence of people.

The independent variable to focus on in this study is music genre. In order to determine whether there are any effects on the dog when listening to different types of music, the dog's environment must be monitored. A controlled experiment would limit the interaction between the dog and other variables.

In this experiment, the researcher can also divide the dogs into two groups, one group performs the music test while the other, the control group, is used as the baseline or standard behavior. The behavior of the control group can be observed along with the treatment group and the differences in the behavior of the two groups analyzed.

What is an experimental control?

Experimental control is the technique used by the researcher in scientific research to minimize the effects of extraneous variables. Experimental control also reinforces the independent variable's ability to alter the dependent variable.

For example, the possibilities of cause and effect are explored in a well-designed and properly controlled experiment when the independent variable (treatment Y) causes a behavioral change in the dependent variable (subject X).

In another example, a researcher fed 20 laboratory rats an artificial sweetener and the researcher observed that six of the rats died of dehydration. Well, the actual cause of death may be artificial sweeteners or an unrelated factor. For example, the water fed to the rats was contaminated, or the rats could not drink enough, or were suffering from an illness.


It is time-consuming and tedious for a researcher to eliminate these possible causes one by one. Therefore, the researcher can make use of an experimental control. Using this method, the researcher can divide the rats into two groups: one group receives the artificial sweetener, the other does not. The two groups will be exposed to similar conditions and monitored in a similar manner. The differences in morbidity that now appear between the two groups can be traced back with certainty to the sweetener.

From the example above, the experimental control is administered as a type of control group. The control group data is then taken as the standard against which every other experimental result is measured.

Purpose and importance of control in experimentation

1. A key purpose of experimental controls is that they allow researchers to eliminate different onesconfounding variables or uncertaintyin their research. A researcher must use an experimental control to ensure that only the variables intended to be changed are changed in the research.

2. Controlled experiments also allow researchers to control for the specific variables that they think might affect the results of the study. The researcher uses a control group when he/she believes that some additional variables may have an impact on the results of the study. This is to ensure that the additional variable is kept constant and possible influences are measured.

3. Controlled experiments establish a standard against which the outcome of a study should be compared and allow researchers to correct potential errors.

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Methods of experimental control

Here are some methods used to achieve control in experimental research

  • Use of control groups

Control groups are required for controlled experiments. Control groups allow the researcher to test for sham and comparable treatments. It will also compare the result of the comparison with the researcher's experimental treatment. The results allow the researcher to understand if the treatment administered caused the result or if other factors such as time or others are involved and if they would have produced the same effects.

As an example of a control group experiment, a researcher conducting an experiment on the effects of color in advertising asked all participants to come to a lab individually. In this laboratory, the environmental conditions remain the same throughout the research.

In order for the researcher to determine the effect of colors in advertising, each of the participants is divided into one of two groups: the control group or the experimental group.

In the control group, the advertising color is yellow to represent the apparel industry, while the experimental group is given blue as the advertising color to also represent the apparel industry. The only difference in these two groups is the color of the ad, other variables are similar.

  • Using Masking (Blinding)

Masking occurs in an experiment when the researcher hides condition assignments from the participants. If the research is double-blind, both the researcher and the participants are groping in the dark. Masking or blinding is mainly used in clinical trials to test new treatments.

Masking as a control measure occurs because researchers can sometimes unintentionally influence participants to act in ways that support their hypotheses. In another scenario, the aim of the study might be revealed to the participants through the study environment and this might influence their answers.

However, masking masks participants from having a deeper knowledge of the research, regardless of whether they are in the control group or the experimental group. This helps to control and reduce biases of the researcher or participants that could influence the results of the study.

  • Use of random assignment

Random assignment or distribution is used to avoid systematic differences between participants in the experimental group and the control group. This helps to evenly distribute irrelevant participant variables, making the comparison between groups valid. Another benefit of random assignment is that it shows the difference between real experiments and quasi-experiments.


How to design a controlled experiment

In order for a researcher to design a controlled experiment, the researcher needs:

  • A hypothesis that can be tested.
  • One or more independent variables can be precisely changed or manipulated.
  • One or more dependent variables can be accurately measured.

When the researcher then designs the experiment, he or she must decide about:

  • How are the variables manipulated?
  • How is control established in the event of possible confounding variables?
  • How large will the samples or participants included in the study be?
  • How are participants distributed across treatment levels?

How you design your experimental controls is of great importance to your experimentsexternal and internal validity.

Examples of controlled experiments

1. A good example of a controlled group would be an experiment to test the effects of a drug. The sample population would be split in two, the group receiving the drug would be the experimental group while the group receiving the placebo would be the control group (note that all variables such as age and gender are the same).

The only significant difference between the two groups will be medication intake. You can tell if the drug is effective or not if the control group and experimental group show similar results.

2. Let's also look at this example. If a researcher wants to determine the influence of different soil types on the germination time of seeds, the researcher can set up four different pots. Each of the pots would be filled with a different type of soil and then seeds can be planted on the soil. After that, each soil pot is watered and exposed to sunlight.

The researcher begins to measure how long it took for the seeds to germinate in different soil types. Control measures for this experiment could be placing some seeds in a pot without filling the pot with soil. The reason behind this control measure is to establish that apart from the soil, no other factor is responsible for germination.

Here the researcher can also control how much sun the seeds are exposed to or how much water they get. The goal is to eliminate all other variables that can affect how quickly seeds germinate.

Experimental controls are important, but it is also important to note that not all experiments should be controlled and that it is still possible to obtain useful data from experiments that are not controlled.

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Problems with controlled experiments

It is true that the best way to test cause and effect relationships is to conduct controlled experiments. However, controlled experiments also have some challenges. Some of them are:

  1. Difficulty controlling for all variables, especially when your research participants are human participants. It may be impossible to keep all additional variables constant, as all individuals have different experiences that may affect their behavior.
  2. Controlled experiments are at risk of low external validity as research results can be limitedextrapolated to a very large population.
  3. Your research may not be able to be related to real-world experiences if it's too controlled, and that will make it difficult for you to apply your findings outside of a controlled setting.

Control group vs. experimental group

There is a thin line between the control group and the experimental group. This line is the treatment condition. As we have already established, the experimental group is the one receiving the treatment, while the control group is the placebo group.

All controlled experiments require control groups because control groups allow you to compare treatments and test for no treatment while comparing the outcome to your experimental treatment.

Therefore, both the experimental group and the control group must conduct a controlled experiment

FAQs on controlled experiments

  • Is the control condition the same as the control group?

The control group differs from the control condition. However, the control condition is administered to the control group.

  • What are positive and negative controls in an experiment?

The negative control is the group where no change or response is expected, while the positive control is the group that receives the treatment with the certainty of a positive result.


While the controlled experiment is beneficial to eliminate external variables in research and focus on the independent variable only to cause an impact on the dependent variable.

Researchers should be careful not to lose the real connection to experiments that are too controlled, and not all experiments should be controlled.

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