On the World Wide Web, a company’s web site is the only point of contact that a company has with anyone who is interested in it. Thus, companies entirely rely on their web presence in order to achieve their online goals, be they commercial or otherwise. This scenario, viewed from an alternative perspective means that the user of a company’s web site will formulate a judgement about that company that is strongly correlated with the way they perceive its web site. If a company’s web site is usable, then it is very likely that a user will achieve his or her goal for using it. This, in turn, will be an active contribution that will help that company towards achieving its own goals. Now, take this successful scenario in view of the circa 2,100 million internet users , and well, you can realize why web site usability is essential for any company with a web presence.
A company typically sets its usability goals through a combination of user profiling, analysis of the main tasks and general business goals. These may be coupled with additional information such as marketing information, competitive analysis, technical support groups and informed opinions . Due to the diversity of such sources, a substantial list of goals is produced. The company then needs to qualitatively and quantitatively specify these goals and then prioritize them so as to determine its usability goals. The latter is the the minimum set of high priority goals that need to be implemented in order for the company to reach the required user performance and satisfaction criteria . The degree to which the company’s web site is successful then depends on whether its user interface balances between the company’s usability goals and those of its users . Not surprisingly, this may sometimes be a very tough endeavor, especially since some marketing practices (such as the definition of the groups that a web site is targeting as well as the company’s goals themselves), may be in conflict with usability aspects of that same web site .
So, what makes a company’s web site usable?
Although the answer to this question largely depends on the nature of the web site and the company’s goals, it is generally acknowledged that web sites which provide the user with useful, well organised, navigable information in a well-structured layout are likely to retain users who access them and also generate repeat visitors  . Still, these general assumptions may be subject of debate. For example, the popular, yet unofficial three-click rule that aims to guide web site content and navigation, states that any information in a web site should be reachable within three clicks or less. Some authors such as Zeldman  support the reasoning behind the three-click rule since they claim that it is based on the same way that people think. Thus, adhering to it helps in developing intuitive, logical and well-structured web sites. Despite of this, authors such as Nielsen and Loranger  claim that during their tests, the users’ability to locate products in an e-commerce web site increased by 600% following the alteration of the design in such a way that it was reachable by four clicks instead of three. Thus, they concluded that adherence to the three click rule typically results in an obscure and overloaded navigation as designers try to make everything reachable within three clicks, often causing more trouble in choosing which link to click than having the users go through an extra, yet more intuitive click .
According to Nielsen and Loranger , the three most important characteristics that distinguish a usable web site are simplicity, naturalness and ease of use. When good usability is implemented in conjunction with good web design characteristics, especially visual attractiveness, it results in a web site that positively affects user behavior and the trust that a user has in the company to whom the web site belongs . This trust is also affected by the user’s perceived usability, that is, the perception that the user has about the usability of a web site before he/she actually makes use of it, although this measure has been found to be strongly correlated with actual web site usability .
What is the effect of a usable web site?
Researchers such as Safavi  have proven that web sites having a user friendly design and an easy-to-use interface increase user satisfaction. At the opposite end of the spectrum, researchers such as Montero et al.  have illustrated how web sites which violate usability conventions confuse users and result in a loss of revenue for the companies behind them. Research also shows that the importance of web site usability increases in relation to the competition that exists within the environment that that web site is operating in. Thus, a web site operating in the very competitive e-commerce environment is more likely to lose a potential customer due to poor usability (often to a competing web site)  rather than a web site that operates in a less competitive environment such as information provision. Surprisingly, this can happen even if that site contains the information, product or service that that user is looking for .
In conclusion, I can find no better quote than Jakob Nielsen’s famous phrase that on the web “the user experiences usability first and pays later” , meaning that users are always at a click away from leaving a web site they are in if they do not find it usable.
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