1. Human Computer Interaction INSY 3020/7976 ENH 670

2. Usability (ISO Definition) The effectiveness, efficiency, and satisfaction with which specified users can achieve specific goals using a particular software application Effectiveness – extent to which a goal or task is achieved Efficiency – amount of effort required to accomplish the goal Satisfaction – level of comfort that users feel when interacting with the product Usability Engineering: The application of HF principles to the design of products

3. User Characteristics Effects on Usability Experience Domain knowledge Cultural Background The physically or Mentally Challenged Age and Gender

4. The Component Model of Usability Guessability Gulf Re-usability System Potential EUPFirst Task Time on Task / Error Rate Learnability Gulf Accounts for the change in the level of task performance with repetition (repeated exposure to the software)

5. Component Model Comprised of: Guessability Learnability Experienced User Performance (EUP) System Potential Re-usability

6. 1. Guessability Effectiveness, efficiency, and satisfaction with which specified users can achieve specific tasks using a particular software for the first time A measure of the cost of the user in using the product to perform a new task for the first time, the lower the cost, the higher the guessability

7. 2. Learnability Effectiveness, efficiency, and satisfaction with which specified users can achieve a component level of performance on specified tasks using a particular software, having completed those tasks once previously Cost to the user in reaching some component level of performance May be a critical factor in situations where training time is short Can distinguish between experienced and inexperienced users Affected by how memorable the first encounter was for the user (lessons learned)

8. 3. Experienced User Performance (EUP) Effectiveness, efficiency, and satisfaction with which specified experienced users can achieve using a particular software package Relatively unchanging performance of someone who has used a product many times before to perform a particular task Critical when after product operation has been learned, users must then perform at a high level Less critical for products used either intermittently or on an on-off basis Pertinent to the use of highly specialized products

9. 4. System Potential The optimum level of effectiveness, efficiency, and satisfaction with which it would be possible to complete a specified task using a particular software package Represents the maximum level of performance that would be theoretically possible (EUP upper limit) Reasons why EUP < System Potential System Potential is a critical issue when it is a limiting factor on EUP

10. 5. Re-usability Refers to the possible decreament in performance after the user has not used the software package for a comparatively long period if time (intermittent user) Can occur if the user has forgotten certain procedures/options associated with proper product use Typically measured as the level of task performance achieved when using the software after a layoff (as a percent of EUP) Dependent on the length of time away and the complexity of the product and task