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Category-size bias

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Category-size bias is a cognitive bias that influences our judgment based on the size of a category or group. It occurs when a larger category or group is perceived to be more diverse than a smaller category or group, even if both contain the same level of diversity. This bias can affect our decision-making in a variety of contexts, including product choices, job candidates, and even our perceptions of social groups. It is important for designers and marketers to be aware of this bias to ensure that their products or messaging are not unfairly influenced by category size.

Table of contents:
  1. What Is the Category-Size Bias?
  2. How to Use the Category-Size Bias in Conversion Rate Optimization
    1. 1. Emphasize the Large
    2. 2. Group Similar Items
    3. 3. Use Visual Comparisons
  3. Conclusion

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Category-Size Bias: What It Is and How to Use It in Conversion Rate Optimization

As a marketer, software developer, or UI/UX designer, you know that getting users to take a specific action or make a purchase on your website is key to its success. But did you know that the way you present your offerings can influence users' decisions?

Enter the category-size bias.

What Is the Category-Size Bias?

The category-size bias is a cognitive bias that describes our tendency to perceive the larger of two options as more valuable or important--regardless of the actual value or importance of each option.

Here's an example:

You're at a buffet and are tasked with choosing between two desserts: a small, decadent chocolate cake and a large fruit tart. Despite the fact that you may personally prefer chocolate cake, you may be more likely to choose the fruit tart due to its larger size.

The category-size bias can be used to influence user behavior on your website. By understanding this bias and implementing it in your design, you can encourage users to take specific actions, such as making a purchase or signing up for a service.

How to Use the Category-Size Bias in Conversion Rate Optimization

So, how can you use the category-size bias to optimize your website for conversions? Here are a few tips:

1. Emphasize the Large

If you want users to perceive one option as more valuable or important, emphasize its size. This can be done by using larger font sizes, bigger images, or making the option physically bigger on the screen.

For example, if you're selling a subscription service with different plan options, make the most expensive plan physically larger on the page. Even if users don't choose the more expensive option, they're more likely to perceive it as valuable due to its larger size.

2. Group Similar Items

By grouping similar items together, you can create the illusion of a larger category, making it seem more valuable to users.

For example, if you're selling clothing on your website, group similar items together, such as all the shirts or all the pants. This creates the impression of a larger category of items, making your offerings seem more valuable and varied.

3. Use Visual Comparisons

One way to leverage the category-size bias is to use visual comparisons to emphasize the difference in size between two options.

For example, let's say you're selling a subscription service with three plans. Instead of simply listing the prices and features, use visual comparisons to show the difference in size and value between each option.

This could be done by using images or icons to represent the features of each plan, or by illustrating the physical size difference between each option.


By understanding and leveraging the category-size bias, you can optimize your website for conversions and encourage users to take specific actions. Remember to emphasize the large, group similar items, and use visual comparisons to create the illusion of value.

With these tips in mind, you can create a website design that utilizes cognitive biases to its advantage, helping you achieve greater success in your marketing efforts.

I hope this brief article has been helpful to you!

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