WEB PERFORMANCE MEETS HUMAN SCIENCES • JUNE 13, 2025.
Hello, Amsterdam! 👋 🇳🇱
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Matheus Albuquerque
↝ 👨💻 STAFF SWE @ MEDALLIA
↝ ⚡ GOOGLE DEVELOPER EXPERT
↝
𝕏
YTHECOMBINATOR
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WEB PERFORMANCE
MEETS HUMAN SCIENCES
MATHEUS ALBUQUERQUE • @ythecombinator
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Preamble
WEB PERFORMANCE MEETS HUMAN SCIENCES
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#question 🤔
What does it mean to be fast?
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#question 🤔
What does it mean to be fast?
If you were to summarize web performance in one
metric, what’d be your pick?
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If you were to summarize
web performance in one
metric, what’d be your
pick?
WEB PERFORMANCE MEETS HUMAN SCIENCES
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WHAT DOES IT MEAN TO BE FAST?
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WHAT DOES IT MEAN TO BE FAST?
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WHAT DOES IT MEAN TO BE FAST?
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#protip 💡
Speed metrics are not a single number.
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AND ALSO…
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#protip 💡
Speed metrics can sometimes be hacked.
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↝ INDICATIONS OF ACTUAL USER BEHAVIOR: TIME SPENT
ON A SITE, BOUNCE RATE, CONVERSIONS, REVENUE,
ETC.
↝ UNFORTUNATELY, MOST OF THESE ARE ALSO PRIVATE
CORPORATE DATA.
“NON-HACKABLE” METRICS
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“NON-HACKABLE” METRICS
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“NON-HACKABLE” METRICS
— STRENGTHENING THE LINK BETWEEN SITE SPEED AND BUSINESS OUTCOMES • ANDY DAVIES, 2018
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“NON-HACKABLE” METRICS
— STRENGTHENING THE LINK BETWEEN SITE SPEED AND BUSINESS OUTCOMES • ANDY DAVIES, 2018
Let’s talk about bias
and frustration.
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“NON-HACKABLE” METRICS
— STRENGTHENING THE LINK BETWEEN SITE SPEED AND BUSINESS OUTCOMES • ANDY DAVIES, 2018
Let’s talk about
measuring
frustration.
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Bias
WEB PERFORMANCE MEETS HUMAN SCIENCES
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“A cognitive bias is a systematic error in thinking that
occurs when people process and interpret information in
their surroundings, in
fl
uencing their decisions and
judgments.”
Judgment Under Uncertainty: Heuristics and Biases • 1982
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COGNITIVE BIASES…
— COGNITIVE BIAS CODEX • JOHN MANOOGIAN III, 2016
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COGNITIVE BIASES…
— COGNITIVE BIAS CODEX • JOHN MANOOGIAN III, 2016
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COGNITIVE BIASES…
HOW WE SEE OUR DATA…
OUTCOME BIAS • CONFIRMATION BIAS • CLUSTERING
ILLUSION • SURVIVORSHIP BIAS
HOW WE PERCEIVE TIME…
INFORMATION PROCESSING • QUEUEING THEORY
HOW USERS JUDGE APPS…
SERIAL-POSITION EFFECT • PEAK-END RULE
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HOW WE SEE OUR DATA…
WEB PERFORMANCE MEETS HUMAN SCIENCES
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ASKING THE USERS
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HOW WE SEE OUR DATA…
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SURVIVORSHIP BIAS
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SURVIVORSHIP BIAS
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SURVIVORSHIP BIAS
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DEVICES & BANDWIDTH
WEB PERFORMANCE MEETS HUMAN SCIENCES
💡 SURVIVORSHIP BIAS
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DEVICES: ADOPTION
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DEVICES: PARSE TIMES
— JAVASCRIPT START-UP PERFORMANCE • 2017
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BANDWIDTH: TECHNOLOGIES
— GSM ASSOCIATION • 2022
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6.07 (MBPS) 44.31 (MBPS)
— THE STATE OF LTE BY OPEN SIGNAL • 2018
BANDWIDTH: LTE SPEED
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BANDWIDTH: DOWNLOAD SPEED
— INTERNET SPEEDS BY COUNTRY • WORLD POPULATION REVIEW, 2025
MEAN DOWNLOAD SPEED 2024 (MBPS)
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BANDWIDTH: AFFORDABILITY
— FIXED-BROADBAND INTERNET BASKET • ITU DATAHUB, 2025
vs. the average
income earned by
each person
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BANDWIDTH: AFFORDABILITY
— FIXED-BROADBAND INTERNET BASKET • ITU DATAHUB, 2025
PORTUGAL MOZAMBIQUE
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BANDWIDTH: AFFORDABILITY
— USE TOOLS TO MEASURE PERFORMANCE • SAM DUTTON
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POLITICAL CONTEXT
💡 SURVIVORSHIP BIAS
WEB PERFORMANCE MEETS HUMAN SCIENCES
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WEB PERFORMANCE MEETS HUMAN SCIENCES
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POLITICAL CONTEXT: CHINA
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POLITICAL CONTEXT: CHINA
— DECODING THE WEB IN CHINA FOR PEAK WEB PERFORMANCE • JODIE CHAN, 2023
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ACCESSIBILITY
WEB PERFORMANCE MEETS HUMAN SCIENCES
💡 SURVIVORSHIP BIAS
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↝ GENERALLY, YOU CAN'T OPERATE A SCREEN READER
WITHOUT A KEYBOARD. SO, ANY OF THE THINGS THAT
IMPACT KEYBOARD USAGE WILL MOST LIKELY AFFECT A
SCREEN READER.
↝ E.G. DELAYED INPUTS, OR FOCUS BEING DROPPED AS
THE PAGE IS UPGRADED WITH JAVASCRIPT.
ACCESSIBILITY
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ACCESSIBILITY: DOM SIZE
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ACCESSIBILITY: REFLOWS
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ACCESSIBILITY: METRICS?
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ACCESSIBILITY
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WRAPPING UP…
WEB PERFORMANCE MEETS HUMAN SCIENCES
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EVEN PATIENCE IS A LOCAL THING…
— UNDERSTANDING EMOTION FOR HAPPY USERS • PHILIP TELLIS, 2020
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HOW USERS JUDGE APPS…
WEB PERFORMANCE MEETS HUMAN SCIENCES
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HOW USERS JUDGE APPS…
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↝ PEAK-END RULE: PEOPLE JUDGE AN EXPERIENCE
LARGELY BASED ON HOW THEY FELT AT ITS PEAK & AT
ITS END.
↝ SERIAL-POSITION EFFECT: PEOPLE RECALL THE FIRST
AND LAST ITEMS IN A SERIES AS BEST, AND THE
MIDDLE ITEMS WORST.
HOW USERS JUDGE APPS…
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↝ RETENTION RATE COULD BE INFLUENCED BY THE BEST &
WORST PERFORMANCE ON FIRST & LATEST PAGES.
↝ CONVERSION RATE: COULD DEPEND ON THE BEST &
WORST PERFORMANCE ON THE PAGE BEFORE THE
CONVERSION.
HOW USERS JUDGE APPS…
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HOW WE PERCEIVE TIME…
WEB PERFORMANCE MEETS HUMAN SCIENCES
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#question 🤔
Do you also feel like time speeds up as you age?
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TIME PERCEPTION
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TIME PERCEPTION: ELEVATORS
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TIME PERCEPTION: AIRPORTS
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TIME PERCEPTION: AIRPORTS
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TIME PERCEPTION: COMPUTERS IN 1968
— RESPONSE TIME IN MAN-COMPUTER CONVERSATIONAL TRANSACTIONS • ROBERT B. MILLER, 1968
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— USABILITY ENGINEERING • JAKOB NIELSEN, 1993
TIME PERCEPTION: COMPUTERS IN 1993
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— MEASURE PERFORMANCE WITH THE RAIL MODEL • GOOGLE
TIME PERCEPTION: CHROME IN 2015
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TIME PERCEPTION: CHROME IN 2015
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TIME PERCEPTION: REACT NOW
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TIME PERCEPTION: REACT NOW
PRIORITY TIMEOUT WHEN
I
m
m
ediate SYNCHRONOUSLY TASKS THAT NEED TO RUN SYNCHRONOUSLY
UserBlocking 250MS RESULTS OF A USER INTERACTION (E.G. A BUTTON CLICK)
Normal 5S UPDATES THAT DON’T HAVE TO FEEL INSTANTANEOUS
Low 10S
TASKS THAT CAN BE DEFERRED BUT MUST STILL COMPLETE
EVENTUALLY (E.G. AN ANALYTICS NOTIFICATION)
Idle NO TIMEOUT
TASKS THAT DO NOT HAVE TO RUN AT ALL (E.G. HIDDEN
OFFSCREEN CONTENT)
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TIME PERCEPTION: REACT NOW
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Frustration
WEB PERFORMANCE MEETS HUMAN SCIENCES
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FRUSTRATION ↝ STRESS
Brainwave analysis from the experiment revealed that
participants had to concentrate up to 50% more when
using websites via the slower connection.
— Study conducted by Foviance on behalf of CA • 2011
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FRUSTRATION ↝ ANXIETY
Delayed web pages caused a 38% rise in mobile users'
heart rates — equivalent to the anxiety of watching a
horror movie alone.
— Ericsson ConsumerLab • 2015
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FRUSTRATION ↝ RAGE
40% of Brits reported that they had become physically
violent toward their computers.
— British Psychology Society • 2009
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FRUSTRATION ↝ RAGE
— TIME IS MONEY • TAMMY EVERTS, 2016
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Measuring
Frustration
WEB PERFORMANCE MEETS HUMAN SCIENCES
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ASKING THE USERS
WEB PERFORMANCE MEETS HUMAN SCIENCES
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WEB PERFORMANCE MEETS HUMAN SCIENCES
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↝ IT’S HARD TO DESIGN IT TO MAKE USERS CHOOSE TO
ANSWER THE SURVEY.
↝ REQUIRES ACTIVE ENGAGEMENT FROM THE USER.
↝ PRONE TO SELECTION BIAS AND THE HAWTHORNE
EFFECT.
ASKING THE USERS
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ASKING THE USERS
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AFFECTIVE COMPUTING
WEB PERFORMANCE MEETS HUMAN SCIENCES
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WEB PERFORMANCE MEETS HUMAN SCIENCES
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AFFECTIVE COMPUTING
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AFFECTIVE COMPUTING
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BEHAVIOR ANALYSIS
WEB PERFORMANCE MEETS HUMAN SCIENCES
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WEB PERFORMANCE MEETS HUMAN SCIENCES
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WEB PERFORMANCE MEETS HUMAN SCIENCES
RAGE CLICKS
💡 BEHAVIOR ANALYSIS
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“Rage clicks occur when users rapidly click (or tap) on
your site or app. Rage clicking is the digital equivalent
of cursing to release frustration.”
Severity and impact of computer user frustration • 2006
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RAGE CLICKS
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RANDOM SCROLLING
WEB PERFORMANCE MEETS HUMAN SCIENCES
💡 BEHAVIOR ANALYSIS
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↝ RAPID SCROLLING, OFTEN THROUGH LARGE CHUNKS.
↝ INDICATES THAT A USER IS ON THE HUNT FOR THEIR
NEXT STEP.
RANDOM SCROLLING
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RANDOM SCROLLING
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WEB PERFORMANCE MEETS HUMAN SCIENCES
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THRASHED CURSOR
WEB PERFORMANCE MEETS HUMAN SCIENCES
💡 BEHAVIOR ANALYSIS
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THRASHED CURSOR
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↝ MOVEMENT COVERING A HIGH DISTANCE TRAVELLED IN A
SHORT AMOUNT OF TIME, WITH NO INTENTIONALITY.
↝ INDICATES IMPATIENCE, DOUBT, DIFFICULTY, OR
ANXIETY.
THRASHED CURSOR
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POSSIBLE ISSUES:
↝ PERFORMANCE: IF IT OCCURS WHILE USERS ARE
WAITING. E.G., A VIDEO BUFFERING OR THE NEXT
ROUTE LOADING.
↝ COGNITIVE LOAD: IF IT OCCURS WHILE THEY'RE
ENGAGED IN AN ACT. E.G., FILLING OUT A FORM,
CREATING/WRITING, OR OTHER CHALLENGING TASK.
THRASHED CURSOR
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THRASHED CURSOR
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CORRELATIONS
WEB PERFORMANCE MEETS HUMAN SCIENCES
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CORE WEB VITALS
WEB PERFORMANCE MEETS HUMAN SCIENCES
💡 CORRELATIONS
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LCP ⁵ RETENTION RATE
— CORE WEB VITALS AND THEIR EFFECT ON USER EXPERIENCE • PHILIP TELLIS, 2025
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CLS ⁵ RELOAD RATE
— CORE WEB VITALS AND THEIR EFFECT ON USER EXPERIENCE • PHILIP TELLIS, 2025
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INP ⁵ RAGE CLICK RATE
— CORE WEB VITALS AND THEIR EFFECT ON USER EXPERIENCE • PHILIP TELLIS, 2025
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UX-IMPACTING METRICS…
WEB PERFORMANCE MEETS HUMAN SCIENCES
💡 CORRELATIONS
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↝ SCROLL EFFECTS WORK.
↝ APP RESPONDS TO CLICKS.
↝ MOST MEANINGFUL VIDEOS/ANIMATIONS RUN.
↝ PRIMARY FEATURE SHOWS UP/IS INTERACTIVE.
↝ COOKIE BANNER SHOWS UP.
TIME UNTIL THE…
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TIME UNTIL THE…
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BUSINESS OUTCOMES
WEB PERFORMANCE MEETS HUMAN SCIENCES
💡 CORRELATIONS
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BUSINESS OUTCOMES…
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BUSINESS OUTCOMES…
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ECONOMICS
PSYCHOLOGY
NEUROSCIENCE
BUSINESS
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Closing
Thoughts
WEB PERFORMANCE MEETS HUMAN SCIENCES
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You can’t
fi
x what you
can’t measure.
#1 of 5
WEB PERFORMANCE MEETS HUMAN SCIENCES
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Always try to correlate
behavior analysis with
contextual metrics and
business outcomes to
tell the full story.
#2 of 5
WEB PERFORMANCE MEETS HUMAN SCIENCES
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Core Web Vitals are a
better starting point
than a
fi
nish line.
#3 of 5
— IN THE BLINK OF AN EYE • TIM KADLEC , 2024
WEB PERFORMANCE MEETS HUMAN SCIENCES
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Acknowledging when
you didn't meet the
user’s expectations can
alleviate negative
perception.
#4 of 5
WEB PERFORMANCE MEETS HUMAN SCIENCES
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WEB PERFORMANCE MEETS HUMAN SCIENCES
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There's probably a
business case for
making your app
faster. But web
performance is about
more than “just”
business.
#5 of 5
WEB PERFORMANCE MEETS HUMAN SCIENCES
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MORE THAN “JUST” BUSINESS!
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MORE THAN “JUST” BUSINESS!
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THAT’S ALL, FOLKS!
THANKS! 👋 🇳🇱
QUESTIONS?
MATHEUS ALBUQUERQUE • @ythecombinator
⬆ ALL THE LINKS!