The following is a summarized list of ROI stats and research based on a recent browse through Randolf Bias & Deborah Mayhew’s Cost-Jusifying Usability: An Update for the Internet Age, Second Edition

10 benefits of working usability into a website (with greatest results being those worked in from project onset):

1. High return on savings. A problem is at least 10 times more expensive to fix after development than if it were addressed in during the design phase with an initial usability analysis.
The rule of thumb in many usability-aware organizations is that the cost-benefit ratio for usability is $1 : $10-$100. Once a system is in development, correcting a problem costs up to 10-100 times more than had the issue been found and addressed from the start.

2. Correcting the 20 easiest flaws yields a usability improvement of 50%. Include usability from the beginning however and the efficiency improvements can be over 700%.
Applying human factors (usability) in the initial design can greatly reduce extensive redesigns, maintenance, and customer support, which can substantially eat away at profits. American Airlines for example, reduced the cost of fixes by 60-90% by correcting usability problems in the design phase.

3. Short term (development) costs are reduced, and long term (user interaction) problems are largely avoided. Taking proactive measures in usability and quality during the initial stages can produce a cost-saving “ripple effect.

4. Reduced maintenance costs. Most maintenance costs are associated with “unmet or unforeseen” user requirements and other usability problems.

5. Save redesign costs. Whether a login improvement saves thousands of people a few seconds every day for a year, or a dialogue box eliminates the number of people who waste an hour of time, the net savings can be dramatic. Sun Microsystems saved $7500 for every $1 spent on usability.

6. Increase revenue. Online shoppers spend most of their time and money on websites with the best usability. Good navigation makes it easier for users to find what they’re looking for and to make a purchase once they’ve found it. Because so many poorly designed websites exist, when customers find one that ‘works’ they tend to return for repeat business and gain trust in the organization.

• You can increase your sales by as much as 225% by providing sufficient product information to your customers at the right time.
• One study estimated that improving the customer experience increases the number of buyers by 40%, and increases the order size by 10% (Creative Good, 2000)
• The magnitude of usability improvements is usually large This is not a matter of increase use by a few percent. It is common for usability efforts to result in a 100% or more increase in traffic or sales (Nielsen 1999)

7. Retain customers (frequency of use).

• More than 83% of users will likely leave a website if they feel they have to make too many clicks to find what they’re looking for (Andersen 2001)
• A bad design can cost a website 40% of repeat traffic. A good design can keep them coming back. A few tests can make the difference (Kalin 1999)

8. Attract more customers (increase appeal).
Staples.com determined that the key to online success and increased market share was to make its e-commerce site as usable as possible. They spent thousands of hours evaluating users’ decision-support needs and online shopping behavior when browsing and buying office products. Methods included data gathering, heuristic testing and usability testing. They achieved these results:

• 67% more repeat customers
• 31-45% reduced drop off rates
• 10% better shopping experience
• 80% increased traffic
• increased revenue

9. Increase market share

• The importance of having competitive edge in usability is even more pronounced for e-commerce sites. Such sites commonly drive away nearly half of repeat business by not making it easy for visitors to find the information they need (Manning 1999)
• The repeat customers are the most valuable: new users at one e-commerce site studied spent and average of $127 per purchase, while repeat users spent almost twice as much, with an average of $251 (Nielsen 1997)

10. Increase success rate and reduce user error. In a study conducted by Jared Spool of 15 large commercial websites, users could only find the information they were seeking 42% of the time even though they were taken to the correct page before they were given the test takes.

Purchase Cost-Justifying Usability: An Update for the Internet Age on Amazon.co.uk