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Impact vs complexity

It’s easy, and potentially disastrous, to conflate these two concepts when prioritizing A/B tests. Let’s avert disaster.


Impact is a measure of how much the test changes conversion rates.

Obviously, you can’t know this until you run the test. (If you did, you wouldn’t bother testing.) So you have to guess.

How to estimate impact

Start by assuming ignorance. Admit that you don’t know, can’t know. It will feel liberating!

Next, gather evidence. Start with these questions:

Are the changes in your variations drastic, or subtle? Drastic changes probably have higher impact.

Have you tested similar changes before? If you tested a copy change elsewhere and saw a huge lift in conversions, that suggests that a copy change can be high impact - for this site, for these visitors.

How bad is the current experience, and the current conversion rate? If the current page is a steaming pile of trash, you can be hopeful that there’s room for improvement. If it’s something you’ve been optimizing for years, it’ll be much harder to have a big impact.


Complexity is a measure of how difficult it is to build, QA, and launch a test. Some teams use its inverse, “ease.” (This is the ‘E’ in the ICE framework.)

This will depend on your team, and the tools you’re using. Complexity is impossible to know until you’ve built the test. So you have to guess.

To come up with an estimate, consider the following questions:

Why it matters

It’s crucial to disentangle these two concepts because impact makes you money, and complexity costs you money. And unless you have evidence to the contrary, there’s no reason to believe they’re correlated.

It’s possible to run easy, high impact tests. Some braggadocious individuals even write blog posts celebrating these victories.

It’s also possible - tragically common - to run complex tests with no impact. I know a heroic developer who once put in 28 hours rebuilding and reordering a 7-step onboarding flow in AngularJS.

Results were flat. $7k down the drain. Hearts were broken.

The worst case scenario is that you and your team come to embrace complexity for its own sake, spending more time to launch fewer tests with lower impact.

What to do

You probably already get this distinction 😇. So please help bring understanding to the rest of the world.

When discussing test ideas with stakeholders and other team members, make sure they get it, too. If you hear someone dismiss a straightforward copy test by saying “Well, it probably won’t have much impact,” set them straight.

“It might not, but we really don’t know. We haven’t tested copy on this page before. Sometimes simple tests have huge impact.”

© 2022 Brian David Hall