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Lostness: A UX metric for measuring if users are lost

September 27, 2017

John Travolta looking lost in Pulp Fiction

The lostness metric can tell you how lost users are when they use your product.

The metric itself is pretty simple as it ranges from zero to one. A high score of lostness means users are having trouble finding what they want. A low score means the opposite, that they are able to find what they want with relative ease. Anything under 0.4 indicates that there are not lost and anything over indicates that they’re lost.

The only way you can measure it is when you know what your users are wanting to do. It’s unlikely analytical data or logs will help you measure it because you don’t know what the users are trying to do.

So the best way to determine it is through usability testing, where you get users to complete a task. This way you know exactly what they’re trying to do and what is the best (quickest) path and how lost they are.

It’s all based on the formula below.

The Formula

The formula for calculating lostness

L = Lostness
N = The number of different screens visited during the task.
S = The total number of screens visited during the task.
R = The minimum number of screens that must be visited to complete a task.

The best way to understand the formula is through an example.

An Example

Let’s pretend that we’re observing a user completing a task in a user test. We ask the user to pick a beer that interests them and view the website of the company that brews the beer.

The task requires the user to visit 3 screens to view the brewer’s website:

  1. Search Beers Screen
  2. Beer Screen
  3. Brewers Website Screen

This means that R is equal to 3 in our lostness formula.

User flow for the optimal path
The optimal path

However, our user visited 7 screens to view the brewer’s website:

  1. Search Beers screen.
  2. View Beer Screen.
  3. About screen.
  4. Back to the View Beer screen.
  5. Back to the Search Beers screen.
  6. Back again to the View Beer screen.
  7. Brewers Website screen.

In our lostness formula, this would result in S being equal to 7. Remember S is the total number of screens visited in the task.

User flow for the path actually taken
The path taken

Also, the user visited the following unique screens in the task:

  1. Search Beers screen.
  2. View Beer screen.
  3. About screen.
  4. Brewers Website screen.

So in our lostness formula, this would result in N being equal to 4. Since N is the number of different screens visited during the task.

This allows us to calculate the lostness of this user during the task so prepare yourself for some math.

A completed version of the lostness formula

By completing the formula we get a lostness value of 0.50. This indicates that the user struggled to access the brewer’s website. Meaning you need to improve your designs so that users can get to their goal.

Let’s wrap up

With this metric, you’re able to measure how lost users get while using your product. This is useful because it’s quantifiable, meaning you can measure any attempts to improve the workflow.

This is the first of a series of UX metrics that I will be sharing over the coming months.

I based this article off my learnings from the book “Validating Product Ideas: Through Lean User Research” by Tomer Sharon. It’s great book with tons of methods for validating product ideas.

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