User-centered design is based on iterative design with the process being evolutionary as it shapes the end product over time, with critical and sometimes decisive input from the users in terms of the product’s performance and preferences. For this process to be used effectively, there should be user input throughout the development cycle of the product and user-centered design to benefit the design process, three principles should be met.
1. An early focus on users and tasks.
This involves an analysis on who the eventual users are going to be, along with an extensive task analysis on the tasks that these users are going to be performing with the product. This data gathering should be structured and systematic, or situations can arise when the data collected would not provide any clear insights into user or task characteristics. It is recommended that the test users be a representative sample of the eventual users of the end product.
2. Empirical measurement of product usage.
Empirical measurements include behavioral indicies of ease of use and learning, for all developmental phases from early paper designs to later product prototypes. Subjective responses on likeability of a product and its features are also informative and sometimes convincing data. It is improper for a designer to assume that if they like and rave about a particular feature of the product, then the users will like and rave about the feature as well.
3. Iterative design for which a product is designed, modified, and tested repeatedly.
Iterative design starts early in the design process and continues until (and usually beyond) a final product is ready for shipment, sale or use by the end user. During early design, user-centered design shapes the product in terms of the tasks its is going to assist the user in completing, the scope in its domain, along with some of the more appealing aesthetic features of the product. During later phases of development iterative design provides the designer to fine tune the product.
User-centered design techniques include focus groups, market surveys, cognitive walkthroughs, heuristic evaluations, usability testing, field (ethnographic studies) and follow-up studies. These techniques are usually performed in the order mentioned and if structured properly can assist the design team in attaining the user-centered design principles. It might not be possible to use each and every one of these techniques, but it is highly recommended that the design team should utilize at least some of these approaches, as it is always better to get some information on product use from the eventual users than none at all.