Measuring Usability
Quantitative Usability, Statistics & Six Sigma by Jeff Sauro

Diagnosing Interaction Problems with Cause and Effect Diagrams

Jeff Sauro • April 5, 2011

It's good to think positively, but sometimes, negative thinking can solve problems more effectively. 

There's no shortage of problems on websites and software. Many of them are interaction problems. 
  • Users can't login
  • Visitors can't find the products in the navigation
  • Customers are calling support
  • Sales are low
  • Conversion rate are down

Fixing Symptoms not Problems

We've all had the experience of fixing the same problem over and over again. When this happens it means you aren't getting to the root cause of the problem. You're likely addressing a surface problem instead of the root cause.

This can happen when we jump right to a solution without fully understanding the problem: 

"Oh, the reason no one is buying is because the button is in the wrong place!"

Cause and Effect Diagrams (aka Fishbone)

One tool that is particularly handy at getting to root causes is the aptly named cause and effect diagram. It is also called the fishbone for its fishy-skeletal shape. 


Download to Power Point

Cause and effect diagrams provide a visual display of possible causes of a problem. Most importantly, they remind us that there are usually multiple causes of problems.  It would be nice if one reason always explained our complex problems, but that's rarely the case.

Fishbones are low-tech--you just need a piece of paper or a white-board for team settings (no need to save the bones from dinner last night).  They are a popular tool used in Six Sigma but you don't need to be a math major to use them.

Using Cause and Effect Diagrams

Here's how' they work.

Step 1. First you define the problem you want to avoid. Let's use the example of low sales of an eBook. Ideally you want this statement to be as specific as possible.  So something like sales are less than then 50 units would define "low" in this case.  The problem goes at the head of the fish.

Step 2.  Brainstorm possible causes for the problem.  For low eBook sales this would be something like
  • Users have to register to purchase
  • Unclear error messages
  • People are unaware of it
  • No advertising
  • Price is too high
  • Too many required fields on payment form
These problems become the bones in the fish. You should think causally (e.g. what causes form abandonment?)

Don't just use the fishbone to outline and don't propose solutions here. For each cause ask "Why does this happen". In fact, ask "why" as many times as you can (sort of like my 3 year old son). 

For example:

Buyers are unware of the product : why?
Low Traffic on the product page: why?
No cross-sell links and no links from articles: why?

Step 3. Sort the causes into clusters, remove duplicates and re-arrange the bones of the fish.

Step 4: Name the main bones something descriptive of the causes: I used Purchasing, Product, Publicity and Pricing (you don't have to alliterate but it sounds better).

Step 5:
Identify areas that need data or investigation: Some causes are obvious (is there any advertising ?) whereas others need data (are users really abandoning the form, how do we know?).

You'll get something that looks like this



Download in Power Point


 
Now that the causes are in the fishbone you'll likely see connections between the causes. Also use this opportunity to continue asking "why" to get at root causes. 

You'll notice that in the example diagram there are many causes of low book sales that have little to do with interaction or usability. It's helpful to get all causes on the fish and then prioritize the fixes based on what's under your control and what's relatively easy to fix.  In this case it's focusing on the Purchasing bone.

You can use the cause and effect diagram at all stages of development to help brainstorm root causes for interaction or other problems. It becomes an excellent input for finding design solutions and turns negative thinking into positive user experiences.

You can download a blank fishbone diagram or the one used in the example to get started.



About Jeff Sauro

Jeff Sauro is the founding principal of Measuring Usability LLC, a company providing statistics and usability consulting to Fortune 1000 companies.
He is the author of over 20 journal articles and 4 books on statistics and the user-experience.
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Posted Comments

There are 1 Comments

May 12, 2011 | Peter Winchester wrote:

Hello, really nice post, easy to read and something to take away and try out immediately. Just one point, your link 'used in the example' is also pointing to your blank template, not the exampleSales one.
Peter 


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