Usability

Usability and User Interface Design

User Interface Design is critical to Usability.
So what factors should be considered when designing a User interface?

8 Characteristics Of Successful User Interfaces read the article.

What is Usability?

"Usability measures the quality of a user's experience when interacting with a product or system whether a Web site, a software application, mobile technology, or any user-operated device."
(adapted from www.usability.gov website)

According to Jakob Nielsen, a leading if somewhat controversial usability expert,
"Studies of user behavior on the Web find a low tolerance for difficult designs or slow sites. People don't want to wait.
People have to be able to grasp the functioning of the site immediately after scanning the home page for a few seconds at most."

Studies on response times state:

0.1 second is about the limit for having the user feel that the system is reacting instantaneously, meaning that no special feedback is necessary except to display the result.
1.0 second is about the limit for the user's flow of thought to stay uninterrupted, even though the user will notice the delay. Normally, no special feedback is necessary during delays of more than 0.1 but less than 1.0 second, but the user does lose the feeling of operating directly on the data.
10 seconds is about the limit for keeping the user's attention focused on the dialogue. For longer delays, users will want to perform other tasks while waiting for the computer to finish, so they should be given feedback indicating when the computer expects to be done. Feedback during the delay is especially important if the response time is likely to be highly variable, since users will then not know what to expect.

These figures have serious implications for web page download times and in turn for file sizes.

STOP PRESS : Study shows - "Average Web Page Size Triples Since 2003 !"
From 2003 to 2008 the average web page grew from 93.7K to over 312K

Here is the Conclusion from the same Study

" Within the last five years, the size of the average web page has more than tripled, and the number of external objects has nearly doubled. ... With the average web page sporting more than 50 external objects, object overhead now dominates most web page delays. Minimizing HTTP requests by using CSS sprites, combining JavaScript or CSS files, ... and converting graphic effects to CSS while still retaining attractiveness, has become the most important skill set for web performance optimizers."

Website Study Read the details of full study.

The impact on Usability is immense, larger files sizes means slower downloads.

A second study has shown that

"Even though computers and connection speeds are getting faster, real-time response time is still the most important factor when designing a website"

Speed is King Read the details of full study.

Exercises -
1. The Web Developers Toolbar has a menu item which will create a speed report.
Tools - View Speed Report
Run the report on some of your pages and 'correct' your pages in line with then report's recommendations.

2. Browse his website http://www.useit.com/ and read the web page "Why This Site Has Almost No Graphics"

How can we measure Usability?

Performance Metric	Usability Measure
Successful completion rates	Effectiveness: Are users able to find information and accomplish tasks?
Time on task (or completion times)	Efficiency: Are users able to accomplish tasks quickly?
Number of pages viewed	Efficiency: How many pages do users visit before successfully finding information on the site?
Pathway or clickstream analysis	Effectiveness: Are users able to select the correct path to find information? Efficiency: How lost do users become in the site?
Subjective satisfaction	Do users enjoy using the Web site?
User comments	Are users frustrated or confused by the site?

Exercise

1. Usability Guidelines

A free book (pdf) on usability. Browse the book to familiarise yourself with the key concepts of usability.

2. Imagine you are looking to buy a new computer online.
Compare the websites of two retail companies web sites.
Using the measures decribed above how do you rate their websites from a usability point of view.
How could they improve.