1 Quality of Service  Quality of Service  Dropped connections  Unavailable websites  Network outages & Delays  Goal is to reduce user frustration  Long delays can result in mistakes

2 Quality of Service  Models of Response-Time Impacts  Response time – number of seconds from the user initiating an action (e.g., ENTER key or mouse-click) until the computer begins to present results (e.g., on display, printer, mobile device)  User think time – the time the user thinks before initiating the next action Model –Initiate –Wait for computer to respond –Watch while the results appear –Think for a while, and initiate again More accurately, users plan while: –Interpreting results –The computer is generating results or retrieving information

3 Quality of Service  Models of Response-Time Impacts User Starts typing User Initiates activity User planning time Computer Begins Response Response time Computer Completes Response User think time

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5 Quality of Service  Short Term and Working Memory  Sensory memory processes perceptual input  Working memory is used to generate and implement solutions  If many facts and decisions are needed to solve a problem, then short term and working memory may become overloaded  Humans learn to cope with complex problems by developing higher-level concepts into single chunk The Working Memory Model (Baddeley and Hitch, 1974)

6 Quality of Service  Short Term and Working Memory  Novices tend to work with smaller chunks until they can cluster concepts into larger chunks  Experts rapidly decompose a complex task into a sequence of smaller tasks  Disruptions cause loss of information in sensory and working memory  Anxiety reduces the size of available memory  If users must record solutions in long term memory (e.g., paper or a complex device), the chances for error increase and the pace of work slows) The Working Memory Model (Baddeley and Hitch, 1974)

7 Quality of Service  Short Term and Working Memory  Challenges to process control (e.g., air traffic control) Task often require integration of information (in short term and working memory) from several sources Need awareness of the total situation  Rapid task performance, low error rates and high satisfaction result from: Users have knowledge of the object and actions needed to solve the problem The solution plan can be carried-out without delay Distractions are eliminated Anxiety is low The is feedback about progress towards the solution Errors can be avoided or, if they occur, can be handled easily

8 Quality of Service  Interaction Speeds Factors involved in choosing the optimal interaction speed –Novices may perform better with slower response times –Novices prefer to work at speeds slower than those chosen by knowledgeable frequent users –When the penalty for error is low, users prefer to work more quickly –When the task is familiar and easily comprehended, users prefer more rapid action –If users have experienced rapid performance previously, they will demand it in future situations Design approaches –Allow users to block interruptions –Providing quick links to specific sites (e.g., bookmarks)

9 Quality of Service  Expectations and Attitudes  For repetitive tasks, uses prefer and will work more rapidly with short response times  For complex tasks, users adapt to working with slow response times with no loss of productivity  In some cases, long response times result in users developing short-cuts, or parallel processing and completing the task in less time  In some cases, fast response times can actually result in more errors  Each task appears to have an optimal pace – response times that are shorter or longer than this pace lead to more errors  Physiologically, higher systolic blood pressure occur with shorter response times  Frustration occurs when delays are twice the anticipated time  Tradeoff: Fast starts vs. Rapid Usage Is it worth a slower start to download a mechanism to improve rapid usage?

10 Quality of Service  Frustrating Experiences  Studies indicate that 46 to 53% of user’s time is wasted  Dropped network connections  Application crashes  Long system response times  Confusing error messages  Based on applications Web browsing (spam/advertisements account for 80% off all s) Viruses –The ILOVEYOU virus caused $5.5 billion of damage

11 Quality of Service  Frustrating Experiences  Spam  Thirty years ago Gary Thuerk sent an to 393 users of Arpanet  Today, spam makes up 80 to 90% of all s sent  Approximately 120 billion messages are sent per day  Today spammers target not just , but also websites, blogs, social networking sites, and cellphones.  $140 billion globally in 2008