🇵🇹 JNation 2025 - Speaker Deck

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WEB PERFORMANCE MEETS HUMAN SCIENCES • MAY 27, 2025. Olá, Coimbra! 👋 🇵🇹

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WEB PERFORMANCE MEETS HUMAN SCIENCES MATHEUS ALBUQUERQUE • @ythecombinator

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MATHEUS ALBUQUERQUE ↝ 👨💻 STAFF SWE @ MEDALLIA ↝ ⚛ CHAIR @ REACT SUMMIT NYC ↝ ⚡ GOOGLE DEVELOPER EXPERT ↝ 𝕏 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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WEB PERFORMANCE MEETS HUMAN SCIENCES If you were to summarize web performance in one metric, what’d be your pick?

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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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“HACKABLE” METRICS…

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WEB PERFORMANCE MEETS HUMAN SCIENCES

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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, AND REVENUE. ↝ UNFORTUNATELY, MOST OF THESE ARE ALSO PRIVATE CORPORATE DATA. “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… 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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↝ OUTCOME BIAS: WHEN WE PICK DATA THAT CONFIRMS PAST OUTCOMES. ↝ CONFIRMATION BIAS: WHEN WE PICK DATA THAT CONFIRMS OUR PRE-EXISTING BELIEFS. ↝ CLUSTERING ILLUSION: WHEN WE SEE PATTERNS WHERE THEY DON'T EXIST. HOW WE SEE OUR DATA…

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HOW WE SAMPLE 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

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BANDWIDTH: AFFORDABILITY — FIXED-BROADBAND INTERNET BASKET • ITU DATAHUB, 2025

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WEB PERFORMANCE MEETS HUMAN SCIENCES

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BANDWIDTH MIX: 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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A11Y 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. SLUGGISH USABILITY, DELAYED INPUT, AND FOCUS BEING DROPPED AS THE PAGE IS UPGRADED WITH JAVASCRIPT. A11Y ∩ PERFORMANCE

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A11Y ∩ PERFORMANCE: DOM SIZE

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A11Y ∩ PERFORMANCE: REFLOWS

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WEB PERFORMANCE MEETS HUMAN SCIENCES

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A11Y ∩ PERFORMANCE: METRICS?

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A11Y ∩ PERFORMANCE: METRICS?

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A11Y ∩ PERFORMANCE

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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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↝ SERIAL-POSITION EFFECT: PEOPLE RECALL THE FIRST AND LAST ITEMS IN A SERIES AS BEST, AND THE MIDDLE ITEMS WORST. ↝ PEAK-END RULE: PEOPLE JUDGE AN EXPERIENCE LARGELY BASED ON HOW THEY FELT AT ITS PEAK & AT ITS END. 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: 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

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TIME PERCEPTION: REACT 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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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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↝ REQUIRES ACTIVE ENGAGEMENT FROM THE USER. ↝ IT’S HARD TO DESIGN THE POPOVER TO MAKE USERS CHOOSE TO ANSWER THE SURVEY (INCREASE SELF- SELECTION). ↝ 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. ↝ PEOPLE HAVE LIMITED ATTENTION SPANS AND SCROLLING FEELS LIKE EXTRA WORK SO THIS CAN QUICKLY CAUSE USERS TO LOSE HOPE. RANDOM SCROLLING

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RANDOM SCROLLING

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WEB PERFORMANCE MEETS HUMAN SCIENCES

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THRASHED CURSOR • WILD MOUSE 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, 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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WEB PERFORMANCE MEETS HUMAN SCIENCES

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BUSINESS OUTCOMES…

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BUSINESS OUTCOMES…

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CORRELATIONS BIAS BEHAVIOR ANALYSIS FRUSTRATION

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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! OBRIGADO! 👋 🇵🇹 QUESTIONS? MATHEUS ALBUQUERQUE • @ythecombinator ⬆ ALL THE LINKS!