Estimate timelines based on actual time taken in past similar tasks, not on plans
Original: eternity4719 · source details
Original author: eternity4719 · Chinese source: · English adaptation: parveen0029. Translation and grade notes ↗
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Cost and benefit at a glance
- Check the cost Cost ↓
- No cost at all. It only requires a few minutes of review to look up how long similar tasks took previously.
- Then the source benefit Benefit ↓
- Students originally expected to finish their papers in 33.9 days, but the actual time taken was 55.5 days. Only 29.7% of them completed their work by their own estimates. When rese…
In plain terms
Students who estimated they would finish a paper in 33.9 days actually took 55.5 days to complete it; only 29.7% of them met their own estimates. Another group of students was asked to first recall how long similar tasks had taken them in the past before making their estimates. The proportion of students who finished on time rose from 29.3% to 60.0% in this group.
This guide's cartoon · show illustration
Enlarge illustrationOriginal illustration with Chinese lettering; the English dialogue is below. Humour is a reading aid, not evidence.
English dialogue
- Tomorrow. Definitely.
- Which step happens today?
Cost: what it takes
No cost at all. It only requires a few minutes of review to look up how long similar tasks took previously.
Benefit: what the source reports
Students originally expected to finish their papers in 33.9 days, but the actual time taken was 55.5 days. Only 29.7% of them completed their work by their own estimates. When researchers asked another group of students to first relate past experiences to the current task before estimating, the proportion of students finishing on time rose from 29.3% to 60.0% compared to the control group. This optimism of underestimating timelines no longer appeared in this group.
Conditions, limits and disagreements
Buehler’s study involved only university students in Canada; it was a single study with a small sample size of 37 participants, with roughly 40 participants in each group. Estimating timelines based on historical data from similar projects is known as reference class forecasting; specific engineering applications are described in Flyvbjerg’s work. Halkjelsvik’s review of multiple studies shows that underestimating timelines is more common than overestimating, though the magnitude of the error varies widely depending on the task and research methodology.
Original references
Original bibliographic titles and links are preserved; some titles are in Chinese.
Buehler, R., Griffin, D., & Ross, M. (1994). Exploring the "planning fallacy": Why people underestimate their task completion times. Journal of Personality and Social Psychology, 67(3), 366–381. https://doi.org/10.1037/0022-3514.67.3.366；Flyvbjerg, B. (2006). From Nobel Prize to project management: Getting risks right. Project Management Journal, 37(3), 5–15. https://doi.org/10.1177/875697280603700302；Halkjelsvik, T., & Jørgensen, M. (2012). From origami to software development: A review of studies on judgment-based predictions of performance time. Psychological Bulletin, 138(2), 238–271. https://doi.org/10.1037/a0025996
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