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The Mind of the User


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Colleen Roller's presentation from the Boston UPA mini conference 2011.

Published in: Technology, Health & Medicine
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The Mind of the User

  1. 1. The Mind of the UserWhen 98% is more than 100%:How number format affects judgment & decisions Colleen Roller UX Matters Columnist On Decision Architecture
  2. 2. Do you know… How well do people understand and interpret numeric data? Does the format of numeric data have an impact? How should we display numeric data?
  3. 3. This presentation Reviews research that reveals how people perceive and use data Suggests UX design principles and best practices
  4. 4. A study Rate the attractiveness of a simple gamble (on a scale from 0-20)  1st group (rating = 9.4)  7 out of 36 chance to win $9  2nd group (rating = 14.9)  7 out of 36 chance to win $9  29 out of 36 chance to lose 5 cents Bateman/Dent/Peters/Slovic/Starmer - 2007
  5. 5. Judgment & decision making Must be able to attach meaning to data Meaning is determined via  Context – a reference point or upper/ lower bound  Comparison – against the contextThe ease with which meaning can be deriveddictates the extent to which data will be used.
  6. 6. A study Which bowl did people prefer: A. 100 beans, 7 of which are red B. 10 beans, 1 of which is red Denes-Raj/Epstein - 1994
  7. 7. A study Which disease is more dangerous? A. Kills 1286 out of every 10,000 people B. Kills 24 out of every 100 people Yamagishi 1997
  8. 8. A study Will a mental patient commit a violent act within 6 months of being discharged from the hospital? A. 20 out of every 100 patients commit a violent act (41% refused to discharge) B. 20% chance that the patient will commit a violent act (21% refused to discharge) Slovic/Monahan/MacGregor - 2000
  9. 9. Quiz Which is more easily understood: A. A 30% chance of rain B. A 3 in 10 chance of rain
  10. 10. 30% chance of rain Common misinterpretations:  It will rain in 30% of the area  It will rain 30% of the time  It will rain on 30% on days like this Gigerenzer/Edwards - 2003
  11. 11. Problems with probability What the doctor said:  You have a 30% - 50% chance of developing a sexual problem What the patient heard:  In 30% - 50% of your sexual encounters, something will go awry Gigerenzer/Edwards - 2003
  12. 12. Summary People tend to  Comprehend frequencies better than probability/percent  20 out of 100, rather than 20%  Focus on the numerator (and ignore the denominator)  9 out of 100 is bigger than 1 out of 10  Different expressions of equivalent data - e.g., 30 out of 1000 is more than 3 out of 10
  13. 13. A study Purchase equipment for use in the event of an airline crash landing: A. Chance of saving 150 lives B. Chance of saving 98% of 150 lives Slovic et al. - 2002
  14. 14. 85% is more than 100% Even 85% of 150 is more than “150”! Slovic et al. - 2002
  15. 15. CalculationsProbability Frequency  1% of car trips result in an  100 out of 10,000 car trips accident. In 55% of the result in an accident. trips that result in an Among the 100 trips that accident, the driver is result in an accident, the drunk. In 5% of the car driver is drunk in 55 of trips that do not result in them. Among the 9900 car an accident, the driver is trips that don’t result in an drunk. If the driver is accident, the driver is drunk drunk, what is the in 500 of them. How many probability of an accident? car trips where the driver is drunk result in an accident?
  16. 16. Study: Rates of return Allocate money across two investment funds – stocks v. bonds  Group A: shown 1-yr rates of return 63%  Group B: shown 30-yr rates of return 81% Benartzi/Thaler, 2001
  17. 17. Data on the page 61% Versus75% Hibbard/Slovic/Peters/Finucane - 2002
  18. 18. No neutral design What information – and how it is presented – drives decision outcomes
  19. 19. Numeric ability Almost half of the general population has difficulty with simple numeric tasks National Adult Literacy Survey
  20. 20. Numeracy Those who are numeric  Readily understand and use numeric data effectively Those who are non-numeric  Informed less by numbers, and more by other non-numeric sources of info
  21. 21. Number format Best Practices
  22. 22. Determine the right criteria Determine what decision criteria people should be using  Highlight them (salience)  Make it easy to evaluate, compute, & attach meaning
  23. 23. Frequency v. probability Convey absolute risks over relative risks  3 out of 1000 will have a stroke is better than  50% higher chance of stroke  Don’t use decimals (.03)
  24. 24. Apples to apples comparisons When presenting various probabilities, keep the denominator consistent  20 out of 1000 compared to 1 out of 1000 is better than  1 out of 50 compared to 1 out of 1000
  25. 25. Attach meaning Use labels to show standard of performance  Example: unacceptable, acceptable, excellent  Labels provide expert guidance and easy mental processing
  26. 26. Mapping A higher number means better quality  Reduces cognitive load  Subtle, but influential
  27. 27. Quiz Which one results in better comprehension and better choices: A. Number of patients per registered nurse B. Number of registered nurses per 100 patients
  28. 28. Variety of visual display
  29. 29. Consecutive v. random Schapira/Nattinger/McHorney - 2001
  30. 30. Placement of solid dots
  31. 31. Conveying small risks To help people understand the meaning of small risks  Show context by providing a range of probabilities and risks for comparison  Example: being hit by a car v. x-rays v. lighting v. asbestos
  32. 32. Emotion v. probability When consequences are marked by strong emotion  All or none – sensitive to the possibility rather than the probability
  33. 33. Final thoughts Determine what info is most important  What should people base the decision on? Design for meaning and ease  Via context and comparison  Facilitate easy computation Test – multiple methods  Test drive, A/B testing, website metrics, think aloud, observe/probe in usability testing
  34. 34. Questions/discussion Colleen Roller UX Matters Columnist on Decision Architecture
  35. 35. Reference articles Simple Tools for Understanding Risks: From Innumeracy to Insight – G. Gigerenzer & A. Edwards, 2003 Numeracy and Decision Making – E. Peters et al., 2006 Numeracy and the Perception and Communication of Risk – E. Peters, 2008 Strategies for Reporting Health Plan Performance Information to Consumers: Evidence from Controlled Studies – J. Hibbard, et al., 2002 Risk as Analysis and Risk as Feelings: Some Thoughts about Affect, Reason, Risk, and Rationality – P. Slovic et al., 2004 Numeracy Skill and the Communication, Comprehension, and Use of Risk- Benefit Information – E. Peters et al., 2007 Reducing the Influence of Anecdotal Reasoning on People’s Health Care Decisions: Is a Picture Worth a Thousand Statistics? - A. Fagerlin et al., 2005 Bringing Meaning to Numbers: The Impact of Evaluative Categories on Decisions – E. Peters et al., 2009 When a 12.86% Mortality is More Dangerous than 24.14%: Implications for Risk Communication – K Yamagishi, 1997