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be designed to match their requirements” (Preece et al.,1995). 18 2.3 Usability Attributes
It is imperative to understand that usability is not a single, one-dimensional property of
a user interface. According to Nielsen (1993) usability has multiple, components and it
is traditionally associated with these five usability attributes:
Efficiency of use
Few and non-catastrophic errors and
Subjective satisfaction. Below, we will discuss all attributes in details.
According to Nielsen (1993) the system should be easy to learn so that the user can
rapidly start getting some work done with the system. Learnability is most likely the
fundamental usability attribute as most systems need to be easy to learn, since the first
experience of users it to learn and understand the system. Although, there are some
certain ways to train the user how to learn system but as general systems needs to be
easy to learn and understand.
The initial ease of learning is most likely the easiest of the usability attributes to
measure with the exception of subjective satisfaction. We can take some novice users to
test any system and can measures the time they takes to reach a specified level of
proficiency in using that system. However, these test users should be future users of that
system. The easiest and most common way to express their proficiency is simply to
state that the users have to be able to complete a certain task successfully. As an
alternative, one can specify that users need to be able to complete a set of tasks in a
certain, minimum time before one will consider them that they have learned that system.
2.3.2 Efficiency of Use:
In order to ensure a high level of productivity, the systems should be efficient to use, so
that once the user has learned the system they can easily use it. System efficiency refers
to the stable performance stage of expert user. Different systems have different level of
efficiency of use, for instance some operating systems are very much complex to
understand and take couple of months to reach an efficiency level. (Nielsen 1993) 19 Experience is the key to measure efficiency; therefore efficiency can be measured with
the help of experienced users. Experience can be defined with the help of users who
have been operating a system for some specific period of time i.e. some months or
years. In addition, experience can also be defined in terms of number of hours spent
using the system. A test case was conducted to measure efficiency, test users are asked
to use the system for a certain number of hours, after which finally it is possible to
define test users as expert users. In addition, efficiency of use can be measured by
taking a group of users and test a system based on some specific tasks and when the
expertise of users will reach to a certain level they would be declared as “experience”
users. (Nielsen 1993)
According to Nielsen (1993) memorability is referred that a system should be easy to
remember, so that a formal user is able to return to the system after some period without
having to relearn everything over again.
Casual users are the third major category of users along with the beginner/novice and
expert users. Casual users are such users who are use a system occasionally as compare
to expert users. As compare to the novice users, casual users have used a system before
therefore they do not need to learn it from scratch; they just need to remember how to
use it based on their previous knowledge. This causal use is generally concern with
utility programs that are just used in few and for between. However, some other
program like quarterly report and annual reports making is also falls in this category.
Easy to remember interface is also vital for users who return after vacation or who have
temporarily stopped using a program. Improvements in learnability often make an
interface easy to remember; however, principally the usability of returning to a system
is different from that of facing it for the first time. (Nielsen 1993)
As compare to other usability features, interface memorability measurement have rarely
been tested in detail. Interface memorability test could be perform with any casual user
who have been out of touch from the system for a specific amount of time and measure
the time he need to perform some typical test task on the previously used system.
Alternatively, it is also possible to conduct a memory test with users after they finished
a test session with the system and ask them to explain the effect of various commands.
The interface score for memorability will be the number of correct answers given by
those casual users. (Nielsen 1993)
2.3.4 Few and non-catastrophic Errors: An error can be defined as, any action that does not accomplish the desired goal. The
system’s error rate can be measured by counting the number of such actions made by 20 system users while performing some particular tasks. Accordingly, system error rates
can be mea...
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- Fall '13
- The Land