The Different Skills Within CRO

CRO (Conversion Rate Optimization) starts with Data! So it’s important to gather both quantitative and qualitative data. Quantitative data is all the data we gather from our website, for example with Google Analytics. The qualitative data comes from user sessions, surveys, and reviews etc.

This part is optional but can be very rewarding. Some companies have a full-time data scientist. The data scientist gets questions from the company, which then are answered according to all the data that’s collected. The data scientist has a data lake/data warehouse for this.

Writing a CRO focused hypothesis

CRO starts when companies realize they can improve their website. It might even go further than only the website. Conversion specialist (somebody who’s specializing in CRO) checks the data and writes a hypothesis on how to improve the website. To be able to write a hypothesis for CRO, the conversion specialist needs knowledge of user experience (UX), data and psychology. I like to write a hypothesis this way (this is what I learned from Online Dialogue):


Example of the hypothesis when used: If we add an extra button next to the call-to-action, then conversions for new users on desktop devices will increase, because of the Hobson’s +1 Choice Effect.

Do you see it? We combine data and science for experimenting. We don’t experiment at random! Metrics next to conversions could be bounce rate, time-on-site, revenue, click-through rate, and page views etc.

Design, experiment duration and sample size

After writing the hypothesis, don’t forget to design (UX) the changes. It might not always be necessary if you change small content, for example. Let the development team build it, or build it yourself.

Before starting to test, you’ve got to know how long it should run and the sample size that’s needed. For this, you can use the Minimum Detectable Effect (MDE). After doing this, it’s time to activate the test.

Traffic for data

To get the data that’s needed, there are different ways to send traffic to your test. Most of the time a combination of SEA (Search Engine Advertising), SEO (Search Engine Optimization), Social Media Advertising, and direct/returning traffic.

For the A/B testing part of CRO, you need lots of data, so do everything you can to get this data. This is the reason why CRO might be hard to do for smaller companies. If you don’t have enough data, you can’t get significant results within 4 weeks, and that’s the maximum time a test should run.

Analyze the results

The data is getting in, you’ve reached the end date, and you have enough data to work with. Now it’s time to analyze the data and evaluate. The first thing to check if the test is significant, always use multiple tools to calculate its significance.

Do a deep dive in the data of the test to check if you found any other data you didn’t expect there. This extra data can be handy when you want to iterate on the test, or it might inspire you for new tests.

If everything is correct and the significance level you’ve decided, most of the time 90%, 95% or 99%, is reached start with the implementation of the test. The question is, can you optimize the part you’ve just tested even further after implementing the changes to the website? Gather data and see if there are still struggles with a specific part of the website. This way you can continue testing.

If you didn’t have enough data to get significant results, you should figure out why and rerun the experiment again. Did the experiment fail? Congratulations, the website has been doing great so far! It might be smart to do the test again with some changes attached to it.

Repeat the steps above

Basically, the cycle starts over and over again, and what isn’t working now might be working a year later. It isn’t strange to do experiment something multiple times over a few years. Companies that do experiments have a big advantage over companies that don’t. The advantage, you ask? You constantly learn about your targeted audience, and you keep improving your website to make it easier for your users.


To be able to do CRO as it’s best to extend you’ll need a team containing people specialized in Psychology, Data, UX design and even a full stack developer. It might seem like a lot of people, but there are CRO specialists that can do all the tasks mentioned above. It won’t be to the extent as when you have a specialist for each specific task within CRO, but in general, it’s a great way of starting with CRO.

The steps I mentioned in this article:

  1. Use data to find flaws in your website
  2. Write a hypothesis containing data, UX and psychology
  3. Create the design for the hypothesis
  4. Calculate the MDE
  5. Build the experiment
  6. Analyze the results including the significance
  7. Evaluate
  8. Repeat the cycle

Final Words

Some aspects didn’t really get the attention they deserved, for example UX design. UX design is not only about how it looks, but also about how you can apply certain psychological theories to the design.

If you have any questions according to this or any of my other articles, feel free to reach out to me. I’m happy to answer all your questions. The same goes for articles, if you have any suggestions feel free to let me know on my social channels or just email me.

Logo Freelance CRO specialist Sander Volbeda

Working remotely from Groningen, the Netherlands. Get in touch and let’s schedule a meeting, no strings attached.

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