Quality of Services (Human Computer Interaction)

With the huge development of World Wide Web there are one problem affected by graphics and network congestion effect which is response time. Time is so precious now for user because a lengthy or unexpected system response time can produce; Frustation, Annoyance and Eventual Anger.

 In contrary if system is too fast then it can result in user less learning, reading with lower comprehension, making more ill-considered decisions and commiting more data-entry errors.

Models of Response-Time Impacts

Response time
The number of seconds it takes from the moment users initiate an activity until the computer presents results on the display

User think time
The number of seconds the user thinks before entering the next action

Designers of response times and display rates in HCI must consider : 

• Complex interaction of technical feasibility
• Cost
• Task complexity
• User expectations
• Speed of task performance
• Error rates
• Error handling procedures

Overall majority of users prefer rapid interactions

• Lengthy response times (15 seconds) are detrimental to productivity
• Rapid response times (1 second or less) are preferable, but can increase errors for complex tasks 

Display Rate

• Alphanumeric displays: The speed in characters per second at which characters appear for the user to read
• World Wide Web Applications: Display rate may be limited by network transmission speed or server performance

Reading textual information from a screen is a challenging cognitive and perceptual task

Conditions for optimum problem solving

• Longer response time causes uneasiness in the user because the penalty for error increases
• Shorter response time may cause the user to fail to comprehend the presented materials
• Progress indicators shorten perceived elapsed time and heighten satisfaction
• Rapid task performance, low error rates, and high satisfaction can come from:
• Other conjectures in choosing the optimum interaction speed

 

 

Expectations and Attitudes

 Users have adapted a working style and expectation based on responses within a fraction of a second. People can detect 8% changes in a 2-4 second response time.

Response-time choke

• A system is slowed down when the load is light and potential performance high
• Makes the response time more uniform over time and across users, avoiding expectations that can’t always be met

Response time across web sites varies
It effects user interest and quality assessment

Three things influence response-time:

• Previous experiences
• The individual's tolerance for delays
• Task complexity

 

User Productivity

Repetitive tasks

• Nature of the task has a strong influence on whether changes in response time alter user productivity
• Shorter response time means users responds more quickly, but decisions may not be optimal
• Goodman and Spence (1981) – reduced response time lead to more productivity
• Teal and Rudnecky (1992) – slower response time lead to more accuracy

Problem solving tasks

• Users will adapt their work style to the response time
• Users will change their work habits as the response time changes
• Grossberg, Wiesen, and Yntema (1976) – the time to solution was invariant with respect to response time

 

Frustating Experience

(Ceaparu et al., 2004) 46% to 53% of users’ time was seen as being wasted because :

• Poor quality of service is more difficult in emerging markets and developing nations
• Email a common application, but also a common source of frustration
• Viruses also a problem

Since frustration, distractions, and interruptions can impede smooth progress, design strategies should enable users to maintain concentration. 

Three initial strategies can reduce user frustration :

• Reduce short-term and working memory load
• Provide information abundant interfaces
• Increase automaticity:

Automaticity in this context is the processing of information (in response to stimuli) in a way that is automatic and involuntary, occurring without conscious control. 

An example is when a user performs a complex sequence of actions with only a light cognitive load, like a driver following a familiar route to work with little apparent effort.