History of Usability
Usability emerged as a result of the intensive research into and use of more advanced technology during the Second World War. It was realised that the adaptation of machines to the human operator increased human-machine reaction, speed and performance. The science soon spread into the field of telecommunications and finally computers. In the U.S. this realisation led to the testing and wholesale redesigning of all digital technology, a usability revolution.Bennett (1979) was the first to use the term usability to describe the effectiveness of Human performance. In the following years a more formal definition was proposed by Shackel (1981) and modified by Bennett (1984). Finally, Shackel (1991) simply defined usability as " the capability to be used by humans easily and effectively, where,

Easily = to a specified level of subjective assessment

Effectively = to a specified level of Human performance

What is Usability?
Usability addresses the full spectrum of impacts upon user success and satisfaction. Usability can be accomplished through user-centered design, although various techniques are employed (eg Psychological perspectives and software driven perspectives). The usability designer provides a point-of-view that is not dependent upon computer programming goals because the usability designer's role is to act as the users' advocate. For example, after interacting with users, the usability designer may identify needed functionality or design flaws that were not anticipated. There are a number of definitions for the quality aspect of usability, including this one from ISO 9241-11:
"The extent to which a product can be used by specified users to achieve specified goals with effectiveness, efficiency and satisfaction in a specified context of use."
"The effectiveness, efficiency and satisfaction with which specified users achieve specified goals in particular environments."


Apart from this definitions there are plethora of information floating around on the net. Usability is one of the focuses of the field of Human-Computer Interaction. If you ask me, Usability is more of making a product/ application / device function simple, easy to use, less time to orient the user, fast to load/start, less complicated and overall to provide the user with a pleasing user experience. Usability, is a generic term which does not restricts its application to specific field overall it can be utilized in various multidisciplinary fields. For eg. you can design a small paper application form in such a simple way, so that the applicant need not come back to you and ask how to fill in the form. The boundries are limitless and there is lot more you can do. Usability has finds it place in Information technology from long time.

Who works in Usability?
The people who are mostly from the disciplines of human factors psychology, social psychology, industrial engineering, technical communications, developmental psychology, information science, human computer interaction engineering and computer science. Apart from the above people Interactive designers, information designers, Information architects, web designers and graphic designers.

Why is Usability important?
Usability is the measure of the quality of a user's experience when interacting with a product or system - whether a web site, software application, mobile technology, or any user-operated device. According to Jakob Neilson, a reknowed web-usability guru, states "On the Web, usability is a necessary condition for survival. If a website is difficult to use, people leave. If the homepage fails to clearly state what a company offers and what users can do on the site, people leave. If users get lost on a website, they leave. If a website's information is hard to read or doesn't answer users' key questions, they leave. Note a pattern here? There's no such thing as a user reading a website manual or otherwise spending much time trying to figure out an interface. There are plenty of other websites available; leaving is the first line of defense when users encounter a difficulty." Above all, if the company wants to sale/services to customers, they should re-think usability before putting their site online. As in todays world various companies are already investing millions of dollars to make their web presence more usable.


Benefits for e-commerce site:
More efficient user tasks lead to better sales
Increased satisfaction leads to increased trust and helps to build a company's brand
Increased effectiveness, satisfaction and trust lead to increased customer loyalty, and to more repeated customers (who, on the average, spend more than first-time customers)
Reduced errors and more effective user activities lead to a higher percent of successful transactions (at same cost of hardware and software)

Benefits for portal site:
An enhanced image of the company, through an increased user satisfaction
A better user experience
Increased user effectiveness


How to evaluate Usability?
There are various methods practiced in the industry they are listed below. The list consists of the best known processes used for evaluation. The methods are :
Think Aloud User testing
Focus Groups




What is user centered design Principles ?
The basic and the most simple principle of User Interface design is to make the user feel in control of the software/system, rather than feeling the controlled by the software/system. The basic forms of interaction your software/system should support are listed below. Directness:
The Design of the software should be such that users can directly manipulate software representations of information. Whether they are dragging an object to relocate it or navigating to a location in a document, users should see how their actions affect the objects on the screen. Visible information and choices also reduce the user's mental workload. Users can recognize a command more easily than they can recall its syntax.Metaphor used to label any element of system, should provide direct and intuitive interface for user tasks. Metaphors used should be in such a way that the user can predict and learn to adapt the system for software based representations. The purpose of using metaphors is to provide a cognitive bridge; the metaphor is not an end in itself. Further more the metaphor used can help the user to associate the meaning with a familiar object, than they remember the syntax for that particular command. Metaphors support user recognition rather than recollection.


Consistency:
It allows the user to map the existing knowledge to new tasks in the new interface. This assists the user to learn new things more easily and comfortably. The main reason for this being, that the user need not spend time remembering and comparing the differences in interaction. By establishing a sense of stability and harmony in the interfaces, consistency helps the user to be familiar and predictable about the interface.Consistency with application, by using the same commands to carry out tasks, that seems similar to the users. In case of printing the document, Print command prints the document; obviously, the user can predict what’s going to happen, when this command is executed or button is clicked. Consistency in visual elements, icons represent the set of instructions, which can be easily visualized by the user. For instance, when using icons in the applications care should be taken so that visual icons comply to the functionality of the application. Consistency in visual terms can also be considered by using icons that represent real life objects. For eg. Using the Trashcan icon for storing deleted files/items from the application, here the trashcan can help user recognize the effect of the delete function.


Forgiveness:
Users most of the times like to explore and learn new things. They always starts to learn things with trial and error method, this behavior initiates another important principle, Forgiveness. The interface provides appropriate set of choices and warns them at various stages about the potential situations, where they can damage the data or system. Moreover, the system makes data reversible and recoverable. There are situations where, even in using the best systems users can commit errors/mistakes by clicking something un-intentionally which can be physical mistake or mental mistakes by making wrong decisions about command or data to select. An effective designed can avoids such situations that can result in errors. It accommodates potential users errors and makes it easy for the user to recover.


Feedback:
Users need to get instant feedback about their actions. Informative and real time feedback is mostly desired. Effective feedback is such that it is timely and is presented as close as the users interaction as possible. There are instances when the user has to wait for a while to let the system process the interaction, at this stage the most disconcerting part would be viewing the blank screen that is unresponsive at that point of time.



Eight Golden Rules of Interface DesignAs a result of Interface Design Studies, Ben Shneiderman proposed a collection of principles that are derived heuristically from experience and applicable in most interactive systems. These principles are common for user interface design, and as such also for web design.
Strive for consistency.
Enable frequent users to use shortcuts.
Offer informative feedback.
Design dialog to yield closure.
Offer simple error handling.
Permit easy reversal of actions.
Provide the sense of control. Support internal locus of control.
Reduce short-term memory load.

Psychology Behind Usability
Baby-Duck-SyndromeBaby Duck Syndrome describes the tendency for visitors to stick to the first design they learn and judge other designs by their similarity to that first design. The result is that users generally prefer systems similar to those they learned on and dislike unfamiliar systems. This results in the usability problems most re-designs have: users, get used with previous designs, feel uncomfortable with new site structure they have to find their way through.
Banner-BlindnessWeb users tend to ignore everything that looks like advertisement and, what is interesting, they’re pretty good at it. Although advertisement is noticed, it is almost always ignored. Since users have constructed web related schemata for different tasks on the Web, when searching for specific information on a website, they focus only on the parts of the page where they would assume the relevant information could be, i.e. small text and hyperlinks. Large colourful or animated banners and other graphics are in this case ignored.
Source: Banner Blindness: Old and New Findings
Cliffhanger-Effect (Zeigarnik-Effect)Human beings can’t stand uncertainty. We tend to find answers to unanswered questions we are interested in as soon as possible. Cliffhanger-effects are based upon this fact; movies, articles and plots with Cliffhanger-effect have an abrupt ending, often leaving with a sudden shock revelation or difficult situation. The effect is often used in advertisement: asking the visitors unanswered and provocative questions advertisers often tend to force them to read the ad, click on the banner or follow a link.
Found out by Bluma W. Zeigarnik in 1927, this effect establishes an emotional connection with readers and is extremely effective in terms of marketing. Visitors can better remember what the ad is about and even smallest details are stored more clearly and precisely. In Web writing the Cliffhanger-effect is also used to bound the visitors to a web-site (e.g. “Grab our RSS-Feed to ensure you don’t miss the second part of the article!”).
Gestalt principles of form perceptionThese principles are the fundamental rules of human psychology in terms of human-computer-interaction-design.
The law of proximity posits that when we perceive a collection of objects, we will see objects close to each other as forming a group.
A real-world example of the law of proximity from MTV Music Awards 2002. Source.
The law of similarity captures the idea that elements will be grouped perceptually if they are similar to each other.
The Law of Prägnanz (figure-ground) captures the idea that in perceiving a visual field, some objects take a prominent role (the figures) while others recede into the background (the ground).
The Macintosh logo can be viewed as a regular happy face and a happy face in profile (looking at a computer screen). Source.
The law of symmetry captures the idea that when we perceive objects we tend to perceive them as symmetrical shapes that form around their centre.
The law of closure posits that we perceptually close up, or complete, objects that are not, in fact, complete.
We perceive the letters ‘I’, ‘B’, and ‘M’ although the shapes we see, in fact, are only lines of white space of differing length hovering above each other. Source.
You can find more information in the article Gestalt principles of form perception
The Self-Reference EffectSelf-reference effect is particularly important for web writing and can dramatically improve the communication between authors and readers. Things that are connected to our personal concept are remembered better than those which aren’t directly connected to us. For instance, after reading an article users better remember the characters, stories or facts they had personal experience with. In Usability the self-reference effect is usually used in terms of web writing and content presented on a web-site.

Usability Glossary: Terms and Concepts

Eye-TrackingEye tracking is the process of measuring either the point of gaze (”where we are looking”) or the motion of an eye relative to the head. eye tracking monitor records every eye movement and highlights the most active areas on the site visually. Eye-tracking studies can help to estimate how comfortable web users are with the web-site they’re browsing through and how quickly they can understand the structure and system behind it. You can find some interesting usability findings from recent eye-tracking study Eyetrack07.
Eye-Tracking: Source.

Fold

The fold is defined as the lowest point where a web-site is no longer visible on the screen. The position of the fold is, of course, defined by the screen resolution of your visitor. The region above the fold (also called screenful) describes the region of a page that is visible without scrolling. Since the fold is seen directly without scrolling, it is often considered as the area which guarantees the highest possible ad click rates and revenues. However, Fold area isn’t that important.
Foveal viewport (Foveal area)

The fovea, a part of human’s eye, is responsible for sharp central vision, which is necessary in humans for reading, watching television or movies, driving, and any activity where visual detail is of primary importance. Foveal area is a small wide space area where your eyes are aimed at and it is the only area where you can perceive the maximum level of detail. Foveal area is a tight area of about two degrees of visual field or two thumbnails held in front of your eyes. This is the place where you’d like to deliver the most important messages of your visitors.
Foveal viewport is important, because outside of this wide screen area how your visitors see your web-pages change dramatically. Inside this area is the only part of your vision with the maximal resolution - only here no eye scanning is necessary.
Gloss

Gloss is an automated action that provides hints and summary information on where the link refers to and where it will take the user once it’s clicked. Hints can be provided via title-attribute of links. From the usability point of view users want to have the full control over everything what is happening on a web-site; clear and precise explanations of internal and outgoing links, supported by sound anchor text, can improve the usability of a web-site.

Graceful Degradation (Fault-tolerance)

Graceful Degradation is the property of a web-site to present its content and its basic features even if some of its components (partly or at all) can’t be displayed or used. In practice it means that web-sites display their content in every possible “fault” scenario and can be used in every configuration (browser, plug-ins, connection, OS etc.) the visitor might have. “Power-users” are still offered a full, enhanced version of the page. For instance, it’s typical to offer alternatives for Multimedia-content (for instance image) to ensure that the content can be perceived if images can’t be displayed.
Granularity

Granularity is the degree to which a large, usually complex data set or information has been broken down into smaller units.