Evaluation is part of what makes usability pervasive, but usability is also fully integrated into every stage of the process.

This process is meant as a paradigm that any actual project should take as an ideal model, but it is not meant to be a inflexible prescription forced onto a project. 

This process handles multiple activities occurring in parallel.  Layout, content development, and technical proof-of-concept designs need to be explored simultaneously as you proceed in the process. 

They may follow separate timetables in larger projects, but the same overall process applies.

Iterative Design
Our design approach is to progressively refine the design through low-cost evaluation at early stages of design, building up to successively more usable designs at each stages of design. 

The most expensive stage is Production, where the final web site is produced.  We want the final design to be as usable as possible so that only minimal changes will be needed at completion. 

At each stage, we want to cycle between refining our design and evaluating our latest refinement, iterating until we’ve achieved a level of usability that we’re satisfied with before continuing to the next stage. 

Evaluation at each stage enables us to incorporate user and client feedback loops to optimize the design.

At each evaluation, we determine whether our design is adequate for continuing on.  We do this by establishing benchmarks, or target usability goals. 

The difficulty with the iterative design approach is that budget and deadlines are typically set before the process, and hence, we may not be able to afford to iterate until we meet our final criteria. 

As an alternative, we may only be able to iterate until our budget has been exhausted, which could be well before our goals are met. 

Of course, the critical questions to ask are: 

If we haven’t met our benchmarks, will the project be successful? 
And if not, should we extend the budget and deadline or should we cancel the project?
So how do we iterate appropriately given these constraints? 

We must:
(1) Plan which types of evaluation to do and how many cycles of iteration will be allotted for each step; and
(2) Leave some slack time in our original schedule to allow for unexpected iterations.

Stages of the Process
The following describes each segment of the Pervasive Usability Process, including the Evaluation component, which can take place throughout the process.

Stage 1.  Requirements Analysis
This is the stage at which you formulate the design problem.  At this stage you determine the target audience and target platforms, user goals, business goals, technical requirements, and so forth. 

This is where user needs and target usability requirements are determined.  Evaluation at this stage usually involves evaluating prior art – previous versions of the product being designed, competitive products, or how people have achieved the same goal without software. 

Common evaluation methods at this stage are competitive analysis, user interviews, and surveys. 

This is the most important step in the process because if you incorrectly identify the goals and parameters of the project, then everything you do after this stage is wasted.

Stage 2.  Conceptual Design
At the Conceptual Design stage, the functionality of the product is worked out.  The design is sketched out at an abstract level of specification that avoids committing to any specific layout or implementation. 

Typical design methods include use cases, task analyses, and information architecture (working out flowcharts and outlines of the system). 

Stage 3.  Mockups and Prototypes
At this stage, visual representations (mockups) or interactive representations (prototypes) of the final design are crated and refined. 

The sole purpose of creating these mockups is to get a chance to evaluate the design early, before the final system is produced. 

The goal is to produce these mockups rapidly and evaluate them efficiently so that they can be refined, elaborated, and reevaluated before you make the final product. 

This can save tremendous time and money by avoiding expensive changes later in the process. 

Stage 4.  Production
At the Production stage, the final product is created.  Final text and graphic content must be developed, and the site must be coded. 

Stage 5.  Launch
Finally, the product is launched and made available to the public.  Just before launch, a final quality testing phase must assure that everything is ready to go online; immediately after launch, the correctness of the site must again be verified. 

Later, a web site will continue to be maintained and refined, and the design process is repeated again from step 1. 

Evaluation
At every stage of development some types of feedback system is essential.  We want to discover as quickly as possible when the design process veers off track. 

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