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Glossary » Design Principles

commons problem

a problem in group behavior where what is best for an individual will actually be harmful for the group as a whole.

If a village has a Commons area for grazing cattle then this Commons area can be a strong…

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in collecting data in user studies, confidentiality guarantees a person that their data will not be released in a way that it can be tracked to them as an individual. Anonymity is slightly different, in that it guarantees that a…

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the principle that things that are related should be presented in a similar way and things that are not related should be made distinctive. Consistency applies across quite varied contexts:

information should be presented in a consistent way: if bold

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control selectivity

the degree to which a control can be manipulated without accidentally activating other controls. A common problem is to position buttons or keys too closely, leading to the wrong button being pressed.

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control sensitivity

the ease with which a control can be activated or set to a certain level. Less sensitive devices require greater effort.

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the degree to which accessing and using an interface is comfortable, and possible without excessive effort, mental or physical. The lack of deterrents to use, including organizational and social deterrents, schedule constraints, system availability, learning threshold, system delays, and prerequisites…

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a systematic approach to design that is established through consistent usage within a design community. Conventions are de facto standards, established not by the dictate of authority, but through implicit agreement and imitation.

Some common conventions include:

placing website navigation

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conversational prop

an object used in a conversation, serving as the focus of the conversation, to provide context, or simply to clarify a point. In general, communication is achieved through 3 primary mechanisms: speech; gestures of the hands, face, and body; and…

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conversion rate

the percentage of people who achieve a given task from a given starting point. On websites, the percentage of people starting at page A who get to page B. So for instance, if 1000 come to a homepage on a…

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the effect that the appearance of a device has on the perception of the person who is using it; it’s “fashion statement”. The degree to which the user can feel attractive and socially acceptable in using the device.

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used to refer to the sharing of information between users, including which objects get shared and how often changes get transmitted between users. Tight coupling refers to situations where almost all information is shared between users and changes are transmitted…

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creeping featurism

the tendency for every new version of software to have more features than the last, in time resulting in an application with an unwieldy number of features that detracts from usability.

Also called “feature cascade”, a much less exciting way…

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criterion testing

user testing that measures user performance to determine whether a target performance level has been reached. Typically a project will begin by determining usability requirements in terms of target performance along various benchmarks, e.g. “starting from the website homepage, the…

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critical mass

the number of people who need to be using a system before it can be successful; often thought of as the number of people contributing in a groupware system to make the value of the system to each individual greater…

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cross-platform compatibility

interoperability or platform-independence; the ability for devices or software applications to work with more than one hardware platform or operating system. Broad compatibility with various systems is critical to having a large market for a product (reaching your entire user…

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customer loyalty

a measure of the success of a design is how frequently the user uses it, how often users return to a website, how often they recommend it to friends, and how often they buy similar products from the same company…

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the ability for a user to set the characteristics of a system to suit their preferences and needs. In desktop software, this is typically done with a “Preferences…” option. Customization may be related to superficial characteristics, such as the skin…

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cut and paste

a simple device for users to move items/data into different parts of a document and between different documents and applications. A user selects an object and selects the “cut” command (from a menu or toolbar). This removes the object from…

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damping factor

how far the pointer has to be moved before a click is considered a drag.

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dead key

a key that modifies the output of the next key to be pressed, such as typing an accent followed by an “e” to get an “é” (Amiga term).

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after running a user study, explaining to a participant what happened and what the study is for, explaining any deception used in the study, asking for any remaining comments or concerns, and ensuring that the participant walks away with no…

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a measure of the time it takes for a message to be transmitted across a network. The variance of the delay is also an important measure. Delay affects the perceived fluidity of a conversation and becomes a more serious problem…

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depth perception

the experience of perceiving a third dimension of depth into a computer screen. For instance, windows add a certain depth by having shadows, and buttons indicate their dimensionality by having beveled edges.

Many different graphical qualities can act as depth…

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descriptive metric

a value that describes some aspect of a system. For instance, if we were trying to automatically evaluate a web page, we might want to rate its “text legibility” based on a measure of the font size used. An automated…

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design for evolution

or plan for obsolescence; organizations and computer systems are always in flux, so it is rare that a design can be made in a one-shot fashion without being terribly expensive to fix when the environment around it outgrows it. Therefore,…

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