What is the best time to create Usability Goals (or Criteria) for your application/website and on what basis?

Question

We know the characteristics of UI being:

• Effectiveness
• Efficiency
• Error Prevention
• Memorability
• Ease of learning
• Satisfaction

While evaluating our design against these measures, it makes sense making them measurable. So that instead of just saying design is good and it meets client's requirements, designers can have this matrix based on results from usability testing whether these characteristics are met or not.

I want to understand what is the best time to create this criteria and how?

Example,

For critical medical service app, 'Error Prevention' criteria should be 'No error' at all.

For complicated software application, (even for advance user), 'Ease of learning' can be 'Consider learnability - Should be able to complete task after going through elearning section which explains how to use particular tool.'

For ticket vendor app, 'Efficiency' should be raising ticket/order in '30 sec'

I have gone through related question Defining “Instantaneous” as part of usability acceptance criteria but I think this discussion is about 'efficiency' only and here I want to understand about other characteristics and also when to create these goals matrics. Should it be at the beginning of the project with the help of Marketing team/stakeholders or just before wireframes creattion; so that wireframes can be molded as per goal.

Answer 1

There are of course general goals that should apply to 99.9% of projects, but the other more specific goals are largely influenced by the development methodology your project is using.

• With a Waterfall model, you should define all of your usability goals upfront, as the project is (in theory at least) designed in one stage and then developed with little chance to test and learn along the way. In reality you may have to make changes as you go, but in theory that doesn't happen with a waterfall model.

• In an Agile or iterative model for a fixed goal or customer, most of your criteria will have to be determined upfront, and small changes can fairly easily be made along the way, as the entire team should be used to constant changes.

• Lean startup: here you really are just searching for a repeatable business model, and are likely to pivot a number of times during the project. So what you thought would be important in the first version, often turns out to be completely different in the 5th version.

It's important to state that Lean startup is an agile methodology, the distinction here is between a project with a fixed goal or customer, and one that is free to change the goal and/or customer.