What is a control group and how can you use one at work?

By Indeed Editorial Team

Published 8 July 2022

The Indeed Editorial Team comprises a diverse and talented team of writers, researchers and subject matter experts equipped with Indeed's data and insights to deliver useful tips to help guide your career journey.

There are various types of work, including marketing, development and research, where testing or experimenting might take place to determine the most successful solution or to understand the impact of an intervention. In these circumstances, the test might include a control group, so it's easier to compare different results. Understanding control groups and how you can use them for business purposes is advantageous for various careers. In this article, we answer the question 'What is a control group?' and discuss how you can use them at work in more detail.

What is a control group?

The answer to 'What is a control group?' is that it's a small group within a larger set of people who receive something other than what you're testing. They're commonly used in a variety of fields, including marketing and scientific research. For example, in medical clinical trials, the control group might receive a placebo or another effective medicine instead of the one the researchers are testing. In marketing, the control group could be a subset of customers who you leave out of a new email marketing campaign.

In both circumstances, having a control group helps to measure how successful the new product or campaign is. You can do this by making comparisons between the behaviour or response of the control group and the group that is testing something new. The larger group that you're testing is commonly known as the test group.

Related: What does a research scientist do? (With responsibilities)

Ways to use a control group at work

You can use a control group in various ways at work depending on what your specialism is. There are several areas of business where using a control group can be beneficial for your work. These are some areas of business where you might encounter control groups:


Marketing professionals frequently use control groups to measure the impact of a new campaign or customer experience. Control groups are the customers who don't receive that campaign or go through a new customer journey. The test group are the customers who do receive that specific campaign. Using a control group means marketing teams can measure the impact of a new campaign and evaluate whether it's a useful strategy.

In some marketing scenarios, there might be other approaches that are more useful than using a control group. For example, an organisation may send a reminder or educational campaign. An alternative is to use A/B testing, where two different versions of a campaign go to two groups of customers to determine which version is more effective and gain insight into customer behaviour. In some other situations, control groups are also part of A/B testing.

Related: Marketing department roles and their responsibilities

Scientific research

Scientific research is an area of work that's well known for using control groups. When researchers are conducting a clinical trial or scientific experiment, participants in the test group have exposure to whatever the scientists are testing, such as a new medical treatment. The researchers can record and compare the responses of both the control group and the rest of the participants. This helps them to form conclusions about how effective the item they're testing is. If the new drug or product is effective, the results from both groups are usually different.

Software development

Control groups can also be useful for software development. Developers also carry out A/B testing to compare different versions of software. They sometimes also include a third control group to determine whether changes are actually necessary. Control groups in these circumstances help developers to identify what already works well before making changes.

Product development

Product development also sometimes uses control groups. Product developers might test a new formula or recipe for a product with one group and provide the original formula or recipe to another. This helps them understand responses to both versions of the product and decide whether the new version is an improvement. It can also help them understand what customers are looking for from their product.

Training development

Organisations can also use control groups when they're developing training. Having a control group that receives no training alongside another group that does can help organisations to evaluate the impact of training on productivity. Comparing the performance of the control group with the group that had further training can indicate whether the training is a worthwhile investment and has the impact the organisation wants.

Related: Types of employee training programmes (with benefits)

Business process development

Organisations that are aiming to streamline or change their business processes can also use control groups to support this work. For example, an organisation that usually has three rounds of interviews can test having only two rounds for some vacancies and also have a control group of vacancies that follow the usual procedure. If subsequent data shows that the quality of new hires is the same despite the shorter process, the organisation is more likely to proceed with this process change.

Benefits of using a control group

There are various benefits to using a control group for testing. Control groups give greater insight into certain behaviours and help to ensure testing accuracy. For example, in marketing, this can be useful for multivariate and A/B campaign testing. Comparing the control group to other groups helps marketing professionals understand the impact of a campaign. Similarly, scientists and researchers can better understand the effects of what they're testing by comparing the results to a control group.

Choosing a control group

To help make the results of your test reliable, it's important to understand how to choose an effective control group. The ideal size depends on the total group size that you're testing. For example, if you're testing one hundred people, you might need a control group that accounts for 20% of the total group size, or twenty people, to give you insightful results. If you're testing 1,000 people, you might only need 10% or one hundred people.

To make the control group effective, it also needs to be random and representational. This is likely to give more accurate results than if every member of your control group is similar. Choosing participants at random is often the most effective way to get a cross-section of results. One method of doing this is to divide the participants into micro-segments and choose individuals randomly from each one. The goal is for the control group to reflect the entire group.

Tips for using control groups

When working with control groups, consider these tips for effectiveness and to get accurate results:

Ensure the control group reflects the whole group

To get balanced results, it's essential that the control group reflect the whole group you're testing. This means that the groups are similar to each other in demographics, behaviour and value to the business. The approach of splitting the whole group into micro-segments can help you achieve this.

Choose the right group size

Choosing the right control group size is also important for accuracy. You need the right number so that the results are reliable. In some circumstances, such as marketing, putting too many people into the control group can mean you miss opportunities. Often between 10% and 20% of the total group is appropriate.

Isolate the test

Isolating the test is important in some circumstances, such as training development and marketing campaigns. This means that you expose both the control group and the entire group to the same stimuli, such as other marketing materials or training materials. When you take this approach, you're only testing one thing at a time, which means you gain clearer insights.

Refresh your control group

Refreshing your control group between tests is a useful tip. Keeping the same group means that you're testing a series of campaigns or methods rather than a specific one. Having the same group is often an effective way to measure the impact of multiple campaigns, but if you want to accurately measure the impact of an individual campaign or intervention, then changing the group each time is preferable.

Use software to support testing

Using online tools and software that support testing with control groups can help. This can be particularly useful for marketing. Having tools that allow you to create control groups and give you the flexibility to individually define these groups helps you to create tests for different types of customers and gain deeper behavioural insights.

Explore more articles