What is tree testing and why is it important for your site’s UX?

Here at WhatUsersDo we’re all about bringing the maximum amount of learning to people at any stage of their UX development. Hence we’re bringing you this series of weekly UX beginner’s guides, aimed to help all the newbies of the UX testing world.

This week: tree-testing!

trees in the snow

Here we’ll be answering the following questions: what is tree testing? What are the benefits? How do I run my own tree testing? How will I possibly stop myself from making a joke about going into a forest, pressing up against a silver birch and saying, “yeah feels pretty woody, now let’s try another one”?

I’ll deal with that last question now: I won’t.

Now let’s answer the rest…

What is tree testing?

We’ve touched on tree-testing before in our beginner’s guide to card-sorting, and although these two methods of user testing share many similarities the method you use to arrive at your results is reversed.

In tree testing, the main categories and subcategories for a website are already established. Test participants are asked to explore these categories in order to find a particular item or piece of content. They click through the various links until they find the category where they expect the item to reside.

Example of a set of categories you might find in a tree test, from Optimal Workshop

During a tree test, you’ll set a number of tasks for your participant to complete.

Here’s an example of a task you might set:

You are on a camping supply website, where would you go to find a sleeping bag? Click through the main menu until you arrive at the location you’d expect to find it.

And here are a few more examples from Optimal Workshop…

set of tasks for a tree test

How is tree testing different from card sorting?

Tree testing is also sometimes known as reverse card sorting. In card sorting, test participants are presented with a list of items (for example, all the products in an online supermarket) and asked to group them in a way that makes sense to them.

Card sorting would logically take place before a tree test. In fact, tree testing is a good way to validate the results from your card sorting exercises.

Why ‘tree’?

The structure of your website looks a bit like a tree. There’s a hierarchy of categories and subcategories (or headings and subheadings, or topics and subtopics depending on your favourite UX terminology).

Only there are less squirrels.

Unless you run a squirrel identification website I suppose.

But then your site structure would probably just consist of two paths – grey and red. Amirite?*

What are the benefits of tree testing?

Tree testing helps identify navigation issues with your site or app. You can analyse where a user would expect to find the information their looking for, and you can make improvements to your site based on this behaviour.

Tree testing will help you validate the effectiveness of your site’s organisation, structuring and labelling. According to Boxes and Arrows, “while open card sorting is a good ‘detective’ technique, it doesn’t yield the final site structure – it just provides clues and ideas.” This is where tree testing comes in.

According to Userzoom, unlike other information architecture tests, tree testing presents participants with realistic task scenarios, so you may learn more about real-world behaviour.

Tree testing is relatively quick, so it’s easier to test variations of a site structure and compare the results. This can also help you provide quantitive results, e.g. Version A had a 47% success rate, compared to Version B’s 22%.

And much like with card sorting, the ultimate benefit is that you’ll be improving your navigation by observing how real users navigate your site rather than just going on assumption.

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What are the disadvantages of tree testing?

Donna Spencer, the information architect responsible for the invention of tree testing, points out that the method tests the top-down organisation of a site and the labelling of its topics. Tree testing therefore concentrates solely on your site structure, so you won’t get any feedback on any other areas of navigation or learn how users may use a blend of functionality on your website.

How do I run tree testing?

Tree testing is typically done remotely, with users on their own computers, in their own environment, completely unmoderated. There are a few different online tools that can help you run tree testing, including of course *cough cough* WhatUsersDo.

If you want to hear more qualitative insight (i.e. a running commentary on why a user is making the decisions they are making) you could organise a moderated session. But these would have to be one-to-one, and you may find your own resources will limit how many you can run.

As opposed to standard user testing, tree testing takes place on a simplified text version of your site that removes everything except the navigable structure of categories and subcategories. This helps keep visual distractions to a minimum and any other methods of navigation (search, breadcrumbs) won’t affect the user’s behaviour or results.

According to NNG, your tree should be a complete list of all your main content categories and all their subcategories. They also point out that even if you’re interested in only testing a specific section of the menu, you shouldn’t exclude the other categories because it assumes that users will know which section to go to.

NNG also recommends providing a tree that is 3, 4 or 5 levels deep and allow your users to be able to go down to the lowest level of subcategories – with each subcategory providing a full list of all options in that area. Just like your actual live website, that your ‘real world’ audience will be exploring.

Tree-testing shouldn’t take longer than 15-20 minutes, and you shouldn’t ask more than 10 tasks. Any more than this and fatigue/boredom will likely set in, as well as familiarity with the site structure. Results may become skewed as users remember where they’ve seen things before.

Userzoom recommends 50 participants for a typical tree test study. This number will “give you the flexibility to exclude participants while maintaining reliable results.” And according to Boxes and Arrows, a good task is clear, specific, and representative of the tasks that actual users will do on the real site.

What should I look for in tree testing results?

Tree testing results tend to be easier to analyse than card sorting results, mainly because of the focus on quantitive data.

According to ExperienceUX, these are some of the key measures you’ll want to look for in your results:

  • Directness: the percentage of users completing the task without hesitation and getting the correct answer first time
  • Success: the percentage of users that completed the task vs. failed attempts
  • Time: the time it took users to complete a task

You can also look at number of attempts to complete a task, as this can indicate where items are difficult to find.

These results should help you decide whether any problems with your structure relate to the organisation of your content or its labelling.

But again, if some of this data isn’t providing enough helpful insight, you can always carry out some moderated tree-tests and ask participants their reasonings in the moment.

*Yes I’m expecting angry comments from the squirrel community. But I’d like to see them work a keyboard or even the simplest emoji based messaging system.

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Main image by Firasat Durrani.

Christopher Ratcliff
Christopher is the Content Marketing Manager of WhatUsersDo. He's also a filmmaker and the editor of wayward pop culture site Methods Unsound. He used to be the deputy editor of Econsultancy and editor of Search Engine Watch.

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