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1 Image: Control Vectors by Vecteezy

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Impact of latency on human-computer interaction

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Impact of latency on human-computer interaction That time Dad broke the stereo

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@tameverts webperf.social/@tammy

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Alarm Vectors by Vecteezy

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usability expert

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student usability expert

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web performance?!?!?

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If you do not consider time a crucial usability factor, you’re missing a huge aspect of the user experience.

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80-90% of end-user response time happens at the front end

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80-90% of end-user response time happens at the front end code

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80-90% of end-user response time happens at the front end code design

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80-90% of end-user response time happens at the front end code design content

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80-90% of end-user response time happens at the front end code design content third parties

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Made pages 1.9 seconds faster, increased conversion rate by 94% 1-second improvement, 14% decrease in bounce rate and 13% increase in conversions Improved Largest Contentful Paint by 31%, increased sales by 8% WPOstats.com

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Waiting is hard

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Passive waiting is harder

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Perception is more important than reality

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Perception is more important than reality

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How do we perceive time?

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When the span between heartbeats is longer, time feels slower* *by milliseconds

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Women tend to underestimate prospective time estimations compared to men, suggesting they may perceive time to be passing by more slowly

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Have you ever thought time is speeding up as you get older?

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Have you ever thought time is speeding up as you get older? It is.

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Over time, the rate at which we process visual information slows down. This is what makes time ‘speed up’ as we grow older.

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Users aged 65+ are 43% slower at using websites than users aged 21-55 nngroup.com/articles/usability-for-senior-citizens/

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86,400 seconds 1,440 minutes

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86,400 seconds 1,440 minutes 1 day

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35 minutes 7 Sharonas

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sex age boredom pain heart rate colour

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How does memory work?

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What is “flow”?

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“…a state in which people are so involved in an activity that nothing else seems to matter; the experience is so enjoyable that people will continue to do it even at great cost, for the sheer sake of doing it” Mihály Csíkszentmihályi Flow: The Psychology of Optimal Experience (1990)

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56 Image by BalashMirzabey on Freepik It can take up to 23 minutes to regain focus after an interruption

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57 Productivity It can take up to 23 minutes to regain focus after an interruption

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58 Productivity Wellbeing It can take up to 23 minutes to regain focus after an interruption

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How does all this apply to how we use technology?

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The average web user believes they waste two days a year waiting for pages to load

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What we say we want vs. what we need 1999 • 8 seconds 2006 • 4 seconds Now • 2 seconds

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A wait longer than 2 seconds breaks concentration and affects productivity Robert Miller Response Time in Man-Computer Conversational Transactions

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A wait longer than 2 seconds breaks concentration and affects productivity Robert Miller Response Time in Man-Computer Conversational Transactions 1968

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65 “We want you to be able to flick from one page to another as quickly as you can flick a page on a book. So, we’re really aiming very, very high here… at something like 100 milliseconds.” Urs Hölzle SVP Engineering, Google

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What do we know about how people perceive speed on the web?

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68 Jakob Nielsen, Website Response Times

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69 When do we start to interact with a page?

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70 Jakob Nielsen, Website Response Times

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“web stress” When apps or sites are slow, we concentrate up to 50% harder to stay on task

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People experience slowness in the moment

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Frustration peaks between 11.5 and 26% during browsing and checkout

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Slowness affects perception of everything

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fast slow

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Content “boring” Visual design “tacky” “confusing” Usability “frustrating” “hard-to-navigate”

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Slowness affects long-term behaviour

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What we think we want does not always make us happy

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“When, as with the Progressive JPEG method, image rendition is a two-stage process in which an initially coarse image snaps into sharp focus, cognitive fluency is inhibited and the brain has to work slightly harder to make sense of what is being displayed.” Dr. David Lewis Chair, Mindlab International

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Slowness is a feeling, not a thought

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“Phone rage”: How people react to slow mobile sites Tealeaf/Harris Interactive

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nicj.net/measuring-continuity/

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nicj.net/measuring-continuity/

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…and so we might be front-end engineers, we might be devs, we might be ops, but what we really are is perception brokers.” Steve Souders Author, High Performance Web Sites “The real thing we are after is to create a user experience that people love and they feel is fast…

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How do you measure perception …at scale?

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Biggest measurement mistakes 1. Not measuring at all You can’t fix what you don’t measure.

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Biggest measurement mistakes 1. Not measuring at all You can’t fix what you don’t measure. 2. Assuming your experience is universal “It’s fast enough on my desktop/phone.”

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Biggest measurement mistakes 1. Not measuring at all You can’t fix what you don’t measure. 2. Assuming your experience is universal “It’s fast enough on my desktop/phone.” 3. Not monitoring continuously Things can change suddenly (e.g., server issues, third parties).

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Biggest measurement mistakes 1. Not measuring at all You can’t fix what you don’t measure. 2. Assuming your experience is universal “It’s fast enough on my desktop/phone.” 3. Not monitoring continuously Things can change suddenly (e.g., server issues, third parties). 4. Not monitoring real users Synthetic measurements are only snapshots.

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Biggest measurement mistakes 1. Not measuring at all You can’t fix what you don’t measure. 2. Assuming your experience is universal “It’s fast enough on my desktop/phone.” 3. Not monitoring continuously Things can change suddenly (e.g., server issues, third parties). 4. Not monitoring real users Synthetic measurements are only snapshots. 5. Not focusing on the right metrics e.g., “Load time” is dated; Core Web Vitals are only available in Chromium browsers

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Biggest measurement mistakes 1. Not measuring at all You can’t fix what you don’t measure. 2. Assuming your experience is universal “It’s fast enough on my desktop/phone.” 3. Not monitoring continuously Things can change suddenly (e.g., server issues, third parties). 4. Not monitoring real users Synthetic measurements are only snapshots. 5. Not focusing on the right metrics e.g., “Load time” is dated; Core Web Vitals are only available in Chromium browsers 6. Looking only at averages or medians Measure at 75th and 95th percentiles to understand the breadth of user experiences.

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Optimize the entire experience 1. Eliminate confusion whenever possible Don Norman, Cofounder/emeritus, Nielsen Norman Group

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Optimize the entire experience 1. Eliminate confusion whenever possible 2. Make the wait appropriate to the results Don Norman, Cofounder/emeritus, Nielsen Norman Group

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Optimize the entire experience 1. Eliminate confusion whenever possible 2. Make the wait appropriate to the results 3. Meet or exceed expectations Don Norman, Cofounder/emeritus, Nielsen Norman Group

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Optimize the entire experience 1. Eliminate confusion whenever possible 2. Make the wait appropriate to the results 3. Meet or exceed expectations 4. End strong Don Norman, Cofounder/emeritus, Nielsen Norman Group

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Made pages 1.9 seconds faster, increased conversion rate by 94% 1-second improvement, 14% decrease in bounce rate and 13% increase in conversions Improved Largest Contentful Paint by 31%, increased sales by 8% WPOstats.com

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107 Create an experience that isn’t just tolerable… it’s delightful

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Time is life

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Thank you! @tameverts webperf.social/@tammy

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Why Waiting Is Torture nytimes.com/2012/08/19/opinion/sunday/why-waiting-in-line-is-torture.html Wrinkles in Subsecond Time Perception Are Synchronized to the Heart onlinelibrary.wiley.com/doi/abs/10.1111/psyp.14270 Sex Differences in Time Perception During Self-paced Running ncbi.nlm.nih.gov/pmc/articles/PMC5065319/ The Color Red Distorts Time Perception for Men, but Not for Women nature.com/articles/srep05899 Why the Days Seem Shorter as We Get Older cambridge.org/core/journals/european-review/article/why-the-days-seem-shorter-as-we-get-older/ Flow: The Psychology of Optimal Experience Mihaly Csikszentmihalyi The Cost of Interrupted Work: More Speed and Stress ics.uci.edu/~gmark/chi08-mark.pdf Response Time in Man-Computer Conversational Transactions dl.acm.org/doi/10.1145/1476589.1476628 Website Response Times nngroup.com/articles/website-response-times/ Progressive Image Rendering: Good or Evil? radware.com/blog/applicationdelivery/wpo/2014/09/progressive-image-rendering-good-evil/ The Psychology of Waiting Lines Don Norman – jnd.org/the-psychology-of-waiting-lines/ Sources