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Useful Features are Not Always Usable

by Kristoffer Bohmann, July 3, 2000

Differences between useful and usable features are discussed and a brief usability framework is presented.

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Usability studies often use the terms useful and usable interchangeably. This article explores the two concepts.

My starting point is that usefulness is concerned with functionality, while the usable concept is about user difficulties in accessing functionality.

Useful features enable users to "do things" by providing the tools needed to perform specific tasks.
In contrast, usable features make "doing" easy. Usable is related to the degree of difficulty understanding and using an information system.

I use the two concepts to assess user performance. I propose that high user performance is achieved when mainstream users use computer systems that are both usable and useful. On the other hand, low user performance is created by two main sources: Lack of features the user needs to solve some task and user difficulties accessing or using features (e.g., comprehension difficulties).

Some examples help clarify the difference. Search results on commercial websites make product search possible. But usability problems frequently occur as search results are presented without the product information users need (exact product title, price, availability), search results are not relevant enough, or too many/few results are displayed per page.

Customer reviews in product detail pages are often regarded as useful design elements because they help users choose which product to buy. However, customer reviews are of little use if they are difficult to use due to uninformative headlines make text scanning difficult, lack of author information make reviews less credible, too many reviews per page may make users frustrated, etc.

Ordering functionality on commercial websites enable online ordering but several usability problems may occur. These include: The "buy this item"-button on product detail pages is not clearly marked which disturb users performing shopping tasks or the shopping cart is labelled with a non-standard word or icon creating confusion for users.

Important synonym concepts. The literature on innovation diffusion use the term relative advantage (Rogers 1995) when speaking of usefulness. Rogers stated that relative advantage is positively related to technology adoption. In the strategic management literature usefulness is often called valuable, where valuable products and product attributes must be provided to gain competitive advantage (e.g., Hamel and Prahalad 1994). The different words describe the same phenomenon: That user needs are satisfied.

The usable dimension is also found in innovation diffusion literature, where the concept low complexity (Rogers 1995) is used to describe usable innovations. Davis (1989) used the term ease of use in his studies on information technology adoption.

Four Scenarios

Several studies report correlations between the usable-useful concepts (e.g., Davis 1989, Keil et al, 1995). So, changes in one dimension can be expected to affect the other. Four types of scenarios are identified and briefly discussed using the usable-useful distinction (Keil et al, 1995).

High usefulness, highly usable. Useful and usable systems are expected to optimize user performance in terms of task time (low) and task error (low).
High usefulness, low usability. Users will be able to perform tasks, but task time will be slower and/or more task errors can be observed.
Low usefulness, highly usable. Users can perform a limited set of tasks in easy ways. However, users may need to do more work manually or using other systems.
Low usefulness, low usability. Users are expected to produce many task errors and task times are long.

Comparative Studies

Competing designs can be assessed using the four system scenarios above. Assessing alternative designs is relevant in several situations, including comparison of two or more website prototypes, comparison between an existing website and a prototype presenting a possible redesign, and comparison of competing web stores, etc.

The comparison is used to discover a superior design. The superior design will be the design that test users regard as more usable and/or useful. There can be some difficulties in determining which of two systems is better, when one system is highly usable yet has low usefulness and the other scores low on usable yet high on useful. However, most design comparisons reveal one design that is clearly superior. Later I shall develop metrics that allow assessment of usability and usefulness of competing designs.

Impact of time

User performance is very likely to change over time due to changes in technological possibilities and user demands (Christensen 1997). For instance, relative usefulness may decrease as new technologies and services emerge. Also relative usability may change due to process improvements (1-click or no-click ordering processes) and improvements in bandwidth enabling faster download speed, larger average screen sizes, and computer displays with improved resolution. Finally, the use of Web technology in new applications such as mobile devices or even microwave owns are likely to create new user demands creating space for new and potentially disruptive solutions.

Research questions

Some very broad areas that needs further attention:

New features. How many new features can be added to a website before mainstream users regard it as less usable, and what factors may make the change happen?
Synergistic features. Some specific combinations of features are likely to have a reinforcing effect on each other that improves user performance. What specific combinations of features can be observed in current Web applications and content?
Features on the Web. Is usable and/or useful concepts more important in Web services compared to other information systems such as software, intranets, and extranets (e.g., due to higher competition and more impatient users)?

References