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Congruence Bias

Congruence Bias


Congruence bias is a human tendency to place too much reliance on direct testing a hypothesis and the neglect of indirect testing. It is similar to confirmation bias because people tend to test what they think is the problem; rather other things that they either like or assume are not problematic.

For example, we might evaluate a registration page which has an image above the form, an offer banner and a long form with a grey background. One optimiser might form a hypothesis that if they remove the image this will improve conversion. So they remove the image and this increases conversion.

But they don’t also test removing the offer banner, reducing the length of the long form, removing the grey background to improve contrast or leaving the image. If they tested making the other changes and retaining the image that might disprove the hypothesis if the conversions went even higher.

Implications for conversion rate optimisation:

The congruence bias can so completely dominate in our thoughts that we fail to recognise that there are alternative hypothesis to consider. You can see this when organisations focus on testing the same things on a regular basis and designers come up with similar ideas to what they have produced in the past. Often it is those things that are not challenged, such as brand guidelines, which represent the greatest opportunity for improvement.

When you evaluate a screen or user journey don’t just develop a single hypothesis. Ensure you develop as many different hypothesis as possible and try to generate hypothesis for areas of a page that you don’t feel are problematic. By doing the later this can help counter congruence bias. However, having a structured approach to optimisation which includes gathering insights from customer research and usability testing should also help to avoid the effects of congruence bias.


Congruence bias can be especially problematic for optimisers who work alone as we can get set in our ways and become too focused on our own theories about what needs changing on a website or app.

Optimisation is most effective when we work collaboratively with designers, developers, marketers, UX and other teams to bring together ideas from a diverse range of people. Further, establishing a structured process for optimisation will also help avoid congruence bias as this encourages evidence-based decision making. Rigorous research and analysis is your best defence against congruence bias.


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