Why Group Sequential Design Means Faster A/B Testing

By Paul Bernier

October 1, 2024

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If your organization runs A/B tests, you probably use the results to make data-backed decisions around your business, product, or services. With the right experiments and reliable results, you can refine the user experience and increase conversions and revenue.

While that sounds great, some organizations running A/B tests find that the process of planning, testing, analyzing, and implementing new features and user experience improvements takes longer than anticipated. But with the right testing methods and tools, your team can get results faster. Tests built with group sequential design can significantly accelerate testing speed without compromising on accuracy or statistical power.

Group sequential design is a statistical method that involves evaluating A/B test results at multiple points during an experiment. One of the main advantages of this method is that, instead of waiting for the full test period to end, you can stop tests early once clear results appear. This allows for quicker decision-making around improvements to your products and services. Your team can also move on to the next round of experiments, which saves some of the time and resources originally allocated for the test.

If you’ve struggled to expand your A/B testing program or run it more efficiently, it might be worth reevaluating your approach. As many as 43% of companies don’t have the right tools for A/B testing, which means choosing a tool with a full set of testing and analytics capabilities (including group sequential design) is one of the most important steps. If you rely on A/B tests to optimize user experiences and improve your products and services, running experiments without the proper tools will lead to missed opportunities, slower improvements, and wasted resources.

So why should your team prioritize a group sequential testing design? With more efficient tests and earlier insights, you could benefit from higher conversion rates and faster organizational growth.

In this blog, we’ll walk through why group sequential design helps you test faster—and why it’s so important for businesses aiming for a stronger ROI on A/B testing.

Reduced Risk of False Positives

A common concern with traditional A/B testing can arise with any experiment: achieving statistical significance. Some organizations worry about the risk of false positives and sample ratio mismatch, and wisely so—seeing results that appear significant but are not could lead your team to make premature product decisions.

In fixed-horizon tests, data analysis is meant to happen only at the end of the testing period. However, in practice, many teams like to “peek” at the results while the test is still running to check if the experiment is performing as expected. This leads to premature conclusions and situations where teams end tests before enough data has been gathered to draw statistically valid conclusions. The result? An increased risk of false positives. When your team bases decisions on incomplete data, they will often have to rerun tests and delay improvements to your website, products, and future tests.

Group sequential design tackles this problem with periodic analysis points built into the structure of the test. These interim checkpoints allow your organization to keep an eye on test data as it comes in.

The result is controlled, real-time monitoring and high statistical sensitivity, which makes it easier to reliably tell if one of the variations is performing well, even with smaller differences between them.

For your organization as a whole, this agile experimentation approach means you’ll encounter fewer errors and spend less time backtracking to rerun tests. Group sequential design helps your team stop tests at the optimal time, saving you effort and expense as you gather user behavior insights for data-driven decisions.

Faster Overall Test Time

With group sequential testing powered by SiteSpect, your team gains access to a new test planner:

The SiteSpect Test Planner enforces proper test planning and an agile testing methodology that evaluates results at predefined checkpoints.

Proper test planning is one of the best ways to make sure that you understand what to look for in every experiment—and it also helps you set up tests correctly in the first place. With an agile testing methodology that allows your team to check in on results at predefined checkpoints, you can blend planned testing frameworks with the reality of incoming results to keep your experimentation program moving forward quickly while producing top-tier, reliable results.

Unlike traditional fixed-horizon tests, where you have to wait until the very end to analyze results, group sequential design lets you act on insights before a test is 100% complete. With built-in checkpoints throughout the test, your team can make data-supported decisions earlier on instead of waiting weeks or months to see if a variation is performing well.

In this case, faster testing doesn’t mean cutting corners. Group sequential design reaffirms experimentation accuracy by allowing you to track data across multiple points in time. While previously you might have waited until the end and hoped for conclusive results, you can now stop tests early once the data reveals a clear winner. This means you get statistically significant outcomes faster, and can confidently move forward rolling out the best version to more users.

Another advantage of group sequential design is the time you can save on obviously inconclusive or underperforming tests and variations. With this testing technique, you can shut down unhelpful tests early, which frees up your time to refocus on more promising ideas and strategies. It’s all part of a broader process that helps you both test faster and make smarter business decisions.

Monitoring

One of the key benefits of group sequential design is the flexibility it offers as your team monitors experiments. The checkpoints during the test give your team opportunities to monitor progress in real time without risking the quality of your results by “peeking”.

If there are any issues with the test, such as uneven samples or incorrect test setup, real-time monitoring helps you catch them early, prevent them from escalating, and ensure everything stays on track as it continues. These checkpoints provide transparency but also help maintain statistical significance by allowing for interim analyses that don’t compromise the validity of your test.

With the option to keep false positives at bay and adjust your tests based on real-time data, group sequential design means your team can stay agile, maintain high statistical standards, and make decisions faster. If you’re looking for the best possible user behavior insights from your A/B tests without giving up accuracy or efficiency, group sequential design is a valuable solution.

Accelerated Adoption of Winning Variations

Once you have test results, it’s time for the next step: implementing winning variations. With group sequential design, where every test runs its shortest possible length, you can adopt the winners faster and optimize user experiences more responsively.

For organizations running an A/B testing program, agility and speed are key. Every day spent waiting for a test to be complete is another day that your business can’t benefit from potential increases in conversions. Group sequential design for tests allows your team to change course quickly as more effective strategies emerge and to iterate on new ones. This ongoing cycle of rapid iteration boosts the efficiency of your experimentation program and encourages continuous improvement.

Final Thoughts

Gathering genuine user behavior insights quickly and accurately is crucial for better conversion rates. Group sequential design offers a statistically solid method to accelerate your A/B testing process without compromising accuracy. By reducing false positives and helping you adopt winning variations faster, this technique saves time and drives more conversions earlier on.

If you’re looking to shift your approach to A/B tests and experimentation, incorporating group sequential design into your strategy could be the solution that helps you connect with your users and stay ahead of the competition.

Ready to see the benefits in action? Request a demo today to learn more about how SiteSpect’s new stats engine can help you implement group sequential testing and start achieving test results faster.

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Paul Bernier

Paul Bernier

Paul Bernier is Vice President of Product Management at SiteSpect. He has a background in website optimization, recommendations, and development, as well as web analytics. He is based in Boston.

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