What Is The "Control Group" In A Controlled Experiment?

Controlled Experiments | Methods & Examples of Control

Published on April 19, 2021 by Pritha Bhandari. Revised on May 20, 2021.

In experiments, researchers manipulate contained variables to examination their effects on dependent variables. In a controlled experiment, all variables other than the contained variable are controlled or held constant so they don't influence the dependent variable.

Controlling variables tin can involve:

holding variables at a constant or restricted level (due east.grand., keeping room temperature stock-still).
measuring variables to statistically control for them in your analyses.
balancing variables across your experiment through randomization (e.g., using a random order of tasks).

Why does control matter in experiments?

Control in experiments is critical for internal validity, which allows you to plant a cause-and-effect relationship between variables.

Case: Experiment

You're studying the effects of colors in advertising. You want to examination whether using green for advertising fast food bondage increases the value of their products.

Your independent variable is the color used in advertisement.
Your dependent variable is the price that participants are willing to pay for a standard fast food repast.

There are many factors that could influence the value of a meal. A controlled experiment is the strongest style to test whether advertising colour really changes how much customers are willing to pay.

Inapplicable variables are factors that you lot're not interested in studying, but that can all the same influence the dependent variable. For strong internal validity, you need to remove their effects from your experiment.

Instance: Inapplicable variables

In your experiment about advertising color and meal value, inapplicable variables include:

Design and clarification of the meal,
Study surroundings (e.k., temperature or lighting),
Participant's frequency of buying fast nutrient,
Participant's familiarity with the specific fast food brand,
Participant's socioeconomic status.

If left uncontrolled, whatsoever of these variables could bear upon how much a participant is willing to spend on a repast, making information technology difficult to determine the true touch of advertizement color on the meal'southward value.

Methods of command

You tin can control some variables past standardizing your data collection procedures. All participants should exist tested in the aforementioned environment with identical materials. Only the contained variable (e.k., ad color) should be systematically changed between groups.

Other extraneous variables can exist controlled through your sampling procedures. Ideally, you'll select a sample that's representative of your target population by using relevant inclusion and exclusion criteria (e.g., including participants from a specific income bracket, and not including participants with color blindness).

By measuring extraneous participant variables (e.k., age or gender) that may affect your experimental results, you tin besides include them in later analyses.

Afterwards gathering your participants, y'all'll need to identify them into groups to test unlike independent variable treatments. The types of groups and method of assigning participants to groups will help you implement control in your experiment.

Control groups

Controlled experiments require control groups. Control groups allow y'all to exam a comparable handling, no treatment, or a false treatment, and compare the outcome with your experimental treatment.

You tin assess whether it's your treatment specifically that caused the outcomes, or whether fourth dimension or any other treatment might have resulted in the same effects.

Case: Control group

In your experiment on the effects of colors in advertising, all participants are invited to come to a lab individually, where environmental conditions are kept the same throughout the study.

To exam the effect of colors in advertising, each participant is placed in i of two groups:

A control group that'southward presented with ruby advertisements for a fast food meal.
An experimental group that's presented with green advertisements for the aforementioned fast food repast.

But the colour of the advertisement is different between groups, and all other aspects of the pattern are the same.

Random consignment

To avoid systematic differences between the participants in your control and treatment groups, you lot should employ random consignment.

This helps ensure that any extraneous participant variables are evenly distributed, assuasive for a valid comparison betwixt groups.

Random assignment is a hallmark of a "true experiment"—it differentiates true experiments from quasi-experiments.

Example: Random assignment

To divide your sample into groups, y'all assign a unique number to each participant. Y'all use a calculator program to randomly identify each number into either a command group or an experimental group.

Because of random assignment, the ii groups have comparable participant characteristics of age, gender, socioeconomic status, etc. That makes it possible to directly compare the results betwixt groups.

Masking (blinding)

Masking in experiments means hiding condition assignment from participants or researchers—or, in a double-blind written report, from both. It'due south often used in clinical studies that test new treatments or drugs.

Sometimes, researchers may unintentionally encourage participants to behave in ways that back up their hypotheses. In other cases, cues in the written report environment may signal the goal of the experiment to participants and influence their responses.

Using masking ways that participants don't know whether they're in the command group or the experimental group. This helps you lot control biases from participants or researchers that could influence your report results.

Example: Masking (blinding)

To apply double blinding, another researcher holds onto information about condition assignment until data drove is complete.

Y'all apply an online survey grade to present the advertisements to participants, and you leave the room while each participant completes the survey on the calculator so that you can't tell which condition each participant was in.

You also hide the research aim from participants by using filler tasks to preclude them from guessing the purpose of the experiment.

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Issues with controlled experiments

Although controlled experiments are the strongest way to examination causal relationships, they also involve some challenges.

Difficult to control all variables

Especially in research with homo participants, it'due south impossible to concord all extraneous variables constant, because every private has different experiences that may influence their perception, attitudes, or behaviors.

Just measuring or restricting extraneous variables allows you to limit their influence or statistically control for them in your study.

Risk of depression external validity

Controlled experiments have disadvantages when information technology comes to external validity—the extent to which your results can exist generalized to wide populations and settings.

The more controlled your experiment is, the less it resembles existent world contexts. That makes it harder to apply your findings outside of a controlled setting.

There's always a tradeoff between internal and external validity. Information technology's important to consider your research aims when deciding whether to prioritize control or generalizability in your experiment.

Frequently asked questions about controlled experiments

What is experimental design?: Experimental design means planning a set of procedures to investigate a relationship between variables. To design a controlled experiment, you demand:

A testable hypothesis

At least i independent variable that can exist precisely manipulated

At to the lowest degree one dependent variable that can be precisely measured

When designing the experiment, y'all determine:

How you volition manipulate the variable(s)

How you will control for any potential confounding variables

How many subjects or samples will be included in the study

How subjects will be assigned to treatment levels

Experimental pattern is essential to the internal and external validity of your experiment.