The Complete Guide to A/B Testing

All the resources you need to get started with A/B testing

What is A/B testing?

A/B testing involves comparing two versions of a web page or application to see which performs better. These variations, known as A and B, are presented randomly to users. A portion of them will be directed to the first version, and the rest to the second. A statistical analysis of the results then determines which version, A or B, performed better, according to certain predefined indicators such as conversion rate.

A/B Testing Definition

A/B testing involves comparing the performance of two or more versions of a web page.

In other words, you can verify which version gets the most clicks, subscriptions, purchases, and so on.  These results can then help you determine an optimal marketing strategy.

Examples of A/B tests

Many of you are looking for ideas for your next A/B tests. If you have been reading the previous chapters, you know there is no magic bullet and that textbook cases are site-specific. However, since you just can’t help yourself, here are some links to a few examples.

What type of websites are relevant for A/B testing ?

Any website can benefit from A/B testing, since they all have a ‘reason for being’ - and this reason is quantifiable. Whether you’re an online store, a news site or a lead generation site, you are aiming to improve your conversion rate, whatever kind of conversion that may be.


The term “lead” is used to mean a sales leads, or a prospective client. Especially relevant here are e-mails sent in order to boost sales. In this case, A/B testing makes use of information about the nature of the people contacted, like their sex or age range.


In a media context, it’s more relevant to talk about "editorial A/B testing".  In industries that work closely with the press, the idea behind A/B testing is to test the success of a given content category - for example, to see if it’s a perfect fit with the target audience.  Here, as opposed to the above example, A/B testing has an editorial function, not a sales one.


Unsurprisingly, the aim of using A/B testing in an e-commerce context is to measure how well a website or online commercial app is selling its merchandise. A/B testing uses the number of completed sales to determine which version performs best. It’s particularly important to look at the home page and the configuration of the product page, but it’s also a good idea to consider all the visual elements involved in completing a purchase (buttons, calls-to-action).

What types of A/B tests should you use?

There are several types of A/B tests. You should choose the one that best fits your particular situation.

  • Classic A/B test. The classic A/B test presents users with two variations of your pages at the same URL. That way, you can compare two or several variations of the same element.
  • Split tests or redirect tests. The split test redirects your traffic towards one or several distinct URLs. If you are hosting new pages on your server, this could be an effective approach.
  • Multivariate or MVT test. Lastly, multivariate testing measures the impact of multiple changes on the same web page. For example, you can modify your banner, the color of your text, your presentation, and more.

In terms of technology, you can:

  • Use A/B testing on websites. A/B testing on the web makes it possible to compare a version A and B of a page. After this, the results are analyzed according to predefined objectives—clicks, purchases, subscriptions, and so on.
  • Use A/B testing for native mobile iPhone or Android applications.   A/B testing is more complex with applications. This is because it is not possible to present two different versions once the application has been downloaded and deployed on a smartphone. Workarounds exist so that you can instantly update your application. You can easily modify your design and directly analyze the impact of this change.
  • Use server-side A/B testing via APIs. An API is a programming interface that enables connection with an application for data exchange. APIs let you automatically create campaigns or variations from saved data.

A/B testing Examples

It is possible to test on multiple devices with solutions like AB Tasty.

A/B testing and conversion optimization

Conversion optimization and A/B testing are two ways for companies to increase profits. Their promise is a simple one: generate more revenues with the same amount of traffic. In light of high acquisition costs and complex traffic sources, why not start by getting the most out of your current traffic?

AB Testing on Amazon
Amazon is very familiar with A/B testing - they're constantly testing to improve UX and conversion rates 

Surprisingly, average conversion rates for e-commerce sites continue to hover between 1% and 3%. Why? Because conversion is a complex mechanism that depends on a number of factors, including the quality of traffic generated, user experience, offer quality, the website’s reputation, as well as what the competition is doing.

E-commerce professionals will naturally aim to minimize any negative impact the interplay of the above elements might have on consumers along the buyer journey.  A variety of methods exist to help them achieve this, including A/B testing, a discipline that uses data to help you make the best decisions.

A/B testing is useful to establish a broader conversion optimization strategy, but it is by no means sufficient all on its own.  An A/B testing solution lets you statistically validate certain hypotheses, but alone, it cannot give you a sophisticated understanding of user behavior. However, understanding user behavior is certainly key to understanding problems with conversion.

A/B testing confirms hypotheses, but alone, it cannot explain user behaviorClick To Tweet

It’s therefore essential to enrich A/B testing with information provided by other means. This will allow you to gain a fuller understanding of your users, and crucially, help you come up with hypotheses to test.

There are many sources of information you can use to gain this fuller picture:

  • Web analytics data. Although this data does not explain user behavior, it may bring conversion problems to the fore (e.g. identifying shopping cart abandonment). It can also help you decide which pages to test first.
  • Ergonomics evaluation. These analyses make it possible to inexpensively understand how a user experiences your website.
  • User test. Though limited by sample size constraints, this qualitative data can provide a myriad of information not otherwise available using quantitative methods.
  • Heatmap and session recording. These methods offer visibility on the way that users interact with elements on a page or between pages.
  • Client feedback. Companies collect large amounts of feedback from their clients (e.g. opinions listed on the site, questions for customer service). Their analysis can be completed by customer satisfaction surveys or live chats.

Recommended solutions for conversion optimization:

Web Analytics

Google AnalyticsPiwikAdobe Analytics AT Internet


Crazyegg Clicky Clicktale

Session Recording

Mouseflow   Session Cam

Live Chat

User Tests

 Usability Hub

User Feedback


How to find A/B test ideas?

Your A/B tests must be complemented by additional information in order to identify conversion problems and offer an understanding of user behavior. This analysis phase is critical, and must help you to create “strong” hypotheses. The disciplines mentioned above will help. A correctly formulated hypothesis is the first step towards a successful A/B testing program and must respect the following rules.

Hypotheses must:

  • be linked to a clearly discerned problem that has identifiable causes
  • mention a possible solution to the problem
  • indicate the expected result, which is directly linked to the KPI to be measured

For example, if the  identified problem is a high abandon rate for a registration form that seems like it could be too long, a hypothesis might be: “Shortening the form by deleting optional fields will increase the number of contacts collected.”

A/B Testing Tools

Use the entire array of solutions available to understand your users’ obstacles

What elements should be tested on a website?

What should you test on your site? This question comes up again and again because companies often don’t know how to explain their conversion rates, whether good or bad. If a company could be sure that their users were having trouble understanding their product, they wouldn’t bother testing the location or color of an add-to-cart button - this would be off topic.  Instead, they would test various wordings of their customer benefits. Every situation is different. Rather than providing an exhaustive list of elements to test, we preferred to give you a framework to identify these elements. Below are some good places to start:

Titles and headers

You can start by changing the title or content of your articles so that they draw people in. Regarding form, a change of color or font can also make a difference.

Call to action

The call to action is a very important button. Color, copy, the position and type of words used ('buy', 'add to cart', 'order', etc.) can have a decisive impact on your conversion rate.

Landing Pages

Lead generation landing pages are quite important to drive your users to take specific actions. Using split testing you can compare complete different versions of these pages with different layout or design.


Images are just as important as text. It is recommended to try different images. For example, if you are a prêt-à-porter e-commerce, verify that photos of clothing articles on models are more popular than photos of the articles alone. Also play on the size and aesthetic of your photos (hue, saturation, brightness, etc.) as well as location (right, left, up, down).

Page structure

The structure of your pages, whether home page or category pages, should be particularly well crafted. You can add a carousel, choose fixed images, change your banner, present a few flagship products on the home page...


Use different algorithms to transform your visitors into customers or increase their cart: similar articles, most-searched products... You can make suggestions to potential customers of things that are likely to interest them.

Business model

Think over your action plan to generate additional profits. For example, if you are selling target merchandise, why not diversify by offering additional products or complementary services?


It is important to create a clear and concise form. You can try modifying a field title, removing optional fields, changing field placement, formatting using lines or columns, etc.


A/B testing on pricing can be delicate. This is because you cannot sell the same product or service for a different price. You’ll need to use a little ingenuity when testing your conversion rate. For example, if you offer services, you can create a low-cost offering with fewer options. If you sell products, offer a different color, shape or material.


You can test different page connections by offering multiple conversion tunnels in one or several parts. For example, you can put the payment mode and information relating to delivery on a single page or separate them into two.

Understanding A/B testing statistics

The test analysis phase is the most sensitive. The A/B testing solution must at least offer a reporting interface indicating the conversions saved by variation, the conversion rate, the percentage of improvement compared with the original and the statistic reliability index saved for each variation. The most advanced ones narrow down the raw data, segmenting results by dimension (e.g. traffic source, geographical location of visitors, customer typology, etc.).

Analyze an A/B test results

Knowing how to analyze the results of a test is critical to making sound decisions.

Before it is possible to analyze test results, the main difficulty involves obtaining a sufficient level of statistical confidence. A threshold of 95% is generally adopted. This means that the probability that result differences between variations are due to chance is very low. The time necessary to reach this threshold varies considerably according to site traffic for tested pages, initial conversion rate for the measured objective and the impact of modifications made. It can go from a few days to several weeks. For low-traffic sites, it is advisable to test a page with higher traffic. Before the threshold is reached, it is pointless to make any conclusions.

All the advice you need to analyze A/B test results and avoid making the wrong choiceClick To Tweet

Furthermore, the statistical tests used to calculate the confidence level (such as the chi-square test) are based on a sample size close to infinity. Should the sample size be low, exercise caution when analyzing the results, even if the test indicates a reliability of more than 95%. With a low sample size, it is possible that leaving the test active for a few more days will greatly modify the results. This is why it is advisable to have a sufficiently sized sample. There are scientific methods to calculate the size of this sample (use our sample size calculator) but, from a practical standpoint, it is advisable to have a sample of at least 5,000 visitors and 75 conversions saved per variation.

There are two types of statistical tests:

  • Frequentist tests. The chi-square method, or Frequentist method, is objective. It allows for analysis of results only at the end of your test. The study is thus based on observation, with a reliability of 95%.
  • Bayesian tests. The Bayesian method is deductive. By taking from the laws of probability, it lets you analyze results before the end of the test. Be sure, however, to correctly read the confidence interval. Check out our dedicated article to see all there is to know about advantages of the Bayesian approach for A/B testing.

Lastly, although site traffic makes it possible to quickly obtain a sufficiently sized sample, it is recommended that you leave the test active for several days to take into account differences in behavior observed by weekday, or even by time of day. A minimum duration of one week is preferable, ideally two weeks. In some cases, this period can even be longer, particularly if the conversion concerns products for which the buying cycle requires time (complex products/services or B2B). As such, there is no standard duration for a test.

Tips and best practices for A/B testing

Below are several best practices that can help you avoid running into trouble. They are the result of the experiences, both good and bad, of our clients during their testing activity.

1. Ensure data reliability for the A/B testing solution

Conduct at least one A/A test to ensure a random assignment of traffic to different versions. This is also an opportunity to compare the A/B testing solution indicators and those of your web analytics platform. This is done in order to verify that figures are in the ballpark, not to make them correspond exactly.

2. Conduct an acceptance test before starting

Do some results seem counter-intuitive? Was the test set up correctly and were the objectives correctly defined? In many cases, time dedicated to acceptance testing saves precious time which would be spent interpreting false results.

3. Test one variable at a time

This makes it possible to precisely isolate the impact of the variable. If the location of an action button and its label are modified simultaneously, it is impossible to identify which change produced the observed impact.

4. Conduct one test at a time

For the same reasons cited above, it is advisable to conduct only one test at a time. The results will be difficult to interpret if two tests are conducted in parallel, especially if they're on the same page.

5. Adapt number of variations to volume

If there is a high number of variations for little traffic, the test will last a very long time before giving any interesting results. The lower the traffic allocated to the test, the less there should be different versions.

6. Wait to have a statistical reliability before acting

So long as the test has not attained a statistical reliability of at least 95%, it is not advisable to make any decisions. The probability that differences in results observed are due to chance and not to the modifications made is very high otherwise.

7. Let tests run long enough

Even if a test rapidly displays statistical reliability, it is necessary to take into account the size of the sample and differences in behavior linked to the day of the week. It is advisable to let a test run for at least a week—two ideally—and to have recorded at least 5,000 visitors and 75 conversions per version.

8. Know when to end a test

If a test takes too long to reach a reliability rate of 95%, it is likely that the element tested does not have any impact on the measured indicator. In this case, it is pointless to continue the test, since this would unnecessarily monopolize a part of the traffic that could be used for another test.

9. Measure multiple indicators

It is recommended to measure multiple objectives during the test. One primary objective to help you decide on versions and secondary objectives to enrich the analysis of results. These indicators can include click rate, cart addition rate, conversion rate, average cart, and others.

10. Take note of marketing actions during a test

External variables can falsify the results of a test. Oftentimes, traffic acquisition campaigns attract a population of users with unusual behavior. It is preferable to limit collateral effects by detecting these kinds of tests or campaigns.

11. Segment tests

In some cases, conducting a test on all of a site’s users is nonsensical. If a test aims to measure the impact of different formulations of customer advantages on a site’s registration rate, submitting the current database of registered users is ineffective. The test should instead target new visitors.

Choosing an A/B testing software

Choosing the best A/B testing tool is difficult. Visit our A/B testing software and split testing tool comparison article for more information about how different vendors compare.

We can only recommend you use AB Tasty. In addition to offering a full A/B testing solution, AB Tasty offers a suite of software to optimize your conversions. You can analyze your users’ behavior with heatmaps and session recording (also known as user session replay). You can also customize your website in terms of numerous targeting criteria and audience segmentation.

In addition to A/B testing, @A/BTasty also helps you understand your website users and personalize their experienceClick To Tweet

But, in order to be exhaustive, and also to provide you with as much valuable information as possible when it comes to choosing a vendor, here are a few articles to help you choose your A/B testing tool with software reviews.

Other forms of A/B testing

A/B testing is not limited to modifications to your site’s pages. You can apply the concept to all your marketing activities, such as traffic acquisition via e-mail marketing campaigns, AdWords campaigns, Facebook Ads, and much more.

The best blogs on A/B testing and CRO

We obviously recommend you read our very own blog, but other experts in international optimization also publish very pertinent articles on the subject of A/B testing and conversion more generally. Here is our selection to stay up to date with the world of CRO.

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