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Optimizely has made it incredibly easy to A/B test any change you want, but experience has shown us that not all tests are equally good. Some changes just don’t affect your site’s visitors in any significant way. Because it’s not practical to test every possible change that comes to mind, it’s important to have a strong hypothesis of why a change will be effective in helping you maximize your site’s goals.


Behavioral Economics and AB Testing

Broadly speaking, behavioral economics is the study of how people make decisions. Behavioral economics takes findings from the field of psychology and cognitive science to explain the times people make decisions that are “irrational,” such as when emotions or imperfect heuristics are used.

If we view the web as a series of decision making processes, then the findings from behavioral economics can be easily applied to web design. Decisions on the web range in complexity and granularity from low-level (should I click this link? Which form option should I choose?) to high-level decisions (should I buy this product? Should I sign up for this service?). Each post in this series will present a different theory from behavioral economics and how it applies to web design and A/B testing.

The Importance of Default Selections

One of the simplest and most robust findings from behavioral economics is that when people are faced with a choice they tend to stick with the default option. This sounds like something that shouldn’t have any effect on people — won’t they always choose whichever option benefits them the most, regardless of the default? Although this intuitively makes sense, numerous studies show the opposite is true. For example, most countries have an option for people to donate their organs upon their death. In America, the default choice is to not donate organs, meaning they must specifically check a box on a form (an “opt-in” system). As a result the consent rate is only about 28%. In contrast, Belgium’s default option is to donate organs (an “opt-out” system), in which about 98% of the population consent to donation [1].

There are many explanations for this behavior. One reason is that making a choice takes effort (even if it’s only checking a box), whereas sticking with the default is effortless. Another reason is when decisions have unclear costs and benefits that are difficult to evaluate (such as organ donation), defaults can imply the “recommended” option, thus saving people the time of thinking through the choice themselves. It also sends the signal that this is the most popular option, reinforcing that there’s safety in numbers.

Web Design

Applying this insight to web pages is fairly straightforward: when presenting people with a choice, provide a default option. This could range from having a radio button on a form already marked to visually highlighting a choice with colors and words (such as “Most Popular Plan!”). Deciding which option to make the default is something you should A/B test, but a common approach is to use existing customer data to preselect the most popular option. For example, if you have multiple pricing tiers you could select the most common one.

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Example of a pricing page with no recommended plan.

Another strategy is to select the option you want your potential customers to select (such as the one that earns you the most profit). This will subtly nudge potential customers towards to select option. For example, Optimizely ran an experiment recommending their Gold plan and saw a 20% increase in signups to that option. After subsequent tests, the team found that highlighting the Gold plan as “popular” not as effective because of how it impacted sign-ups to other plans.

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Example of a pricing page recommending the “plus” plan.

Recommending pricing plans is just one way of many that default options can be applied to web design. Consider experimenting with your forms, account settings, preferences, or anything else that comes to mind. In the end there’s no right answer and you should test everything to find the most optimal option. At least now you’ll have a strong hypothesis driving your changes!

For more on the subject of defaults and behavior, check out this paper:

[1] “Do defaults save lives?” by Eric J. Johnson and Daniel Goldstein (2003)

Do you use default selections on your site? How have they impacted your visitor’s behavior? Leave a comment with your success story!