Usability testing is a means for measuring how well people can use some human-made object (such as a web design, a computer user interface, a document, or a device) for its intended purpose, i.e. usability testing measures the Usability of the object. Usability testing focuses on a particular object or a small set of objects, whereas general human-computer interaction studies attempt to formulate universal principles.

If usability testing uncovers difficulties, such as people having difficulty understanding instructions, manipulating parts, or interpreting feedback, then developers should improve the design and test it again. During usability testing, the aim is to observe people using the product in as realistic a situation as possible, to discover errors and areas of improvement. Designers commonly focus excessively on creating designs that look cool , compromising usability and functionality. This is often caused by pressure from the people in charge, forcing designers to develop systems based on management expectations instead of people s needs. A designers primary function should be more than appearance, including making things work with people.

Caution: simply gathering opinions is not usability testing -- you must arrange an experiment that measures a subject s ability to use your document. [http://jerz.setonhill.edu/design/usability/intro.htm 1]

Rather than showing users a rough draft and asking, Do you understand this , usability testing involves watching people trying to use something for its intended purpose. For example, when testing Instructions for assembling a toy, the test subjects should be given the instructions and a box of parts. Instruction phrasing, illustration quality, and the toy s design all affect the assembly process.

Setting up a usability test involves carefully creating a scenario, or realistic situation, wherein the person performs a list of tasks using the product being tested while observers watch and take notes. Several other test instruments such as scripted instructions, paper prototypes, and pre- and post-test questionnaires are also used to gather feedback on the product being tested. For example, to test the attachment function of an E-mail program, a scenario would describe a situation where a person needs to send an e-mail attachment, and ask him or her to undertake this task. The aim is to observe how people function in a realistic manner, so that developers can see problem areas, and what people like. The technique popularly used to gather data during a usability test is called a think aloud protocol.

=What to measure=

Usability testing generally involves measuring how well test subjects respond in four areas: time, accuracy, recall, and emotional response. The results of the first test are the baseline or control measurement; all subsequent tests are compared to the baseline.

In the early 1990s, .

The claim of Five users is enough was later described by a mathematical model (Virzi, R.A., Refining the Test Phase of Usability Evaluation: How Many Subjects is Enough Human Factors, 1992. 34(4): p. 457-468.) which states for the proportion of uncovered problems U

U = 1-(1-p)^n

where p is the probability of one subject identifying a specific problem and n the number of subjects (or test sessions). This model shows up as an asymptotic graph towards the number of real existing problems (see figure below).

In later research Nielsen s claim has eagerly been questioned with both s (Caulton, D.A., Relaxing the homogeneity assumption in usability testing. Behaviour & Information Technology, 2001. 20(1): p. 1-7.). Most researchers today agree that in many applications a sample size quite larger than five is required to detect a satisfying amount of usability problems.

Bruce Tognazzini advocates close-coupled testing : Run a test subject through the product, figure out what s wrong, change it, and repeat until everything works. Using this technique, I ve gone through seven design iterations in three-and-a-half days, testing in the morning, changing the prototype at noon, testing in the afternoon, and making more elaborate changes at night. [http://www.asktog.com/columns/001closecoupledtesting.html 4] This testing can be useful in research situations

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