Card rules · 2026-10-29
Your Fastest Card Answer Is Not Your Average
Three equivalent card-identification exercises take 10, 20 and 30 seconds. The fastest answer takes 10 seconds. The arithmetic mean is 20 seconds. Both figures are correct, but they…
Three equivalent card-identification exercises take 10, 20 and 30 seconds. The fastest answer takes 10 seconds. The arithmetic mean is 20 seconds. Both figures are correct, but they describe different things.
Keep the measure attached to its name
A personal best selects one extreme observation. An average combines the included observations. Replacing “best time” with “usual time” overstates what the fastest attempt demonstrates. Even the mean of three attempts is only a description of that small set, not a guarantee about future performance.
Check comparability before combining
Were all attempts completed under the same conditions? A hand previously seen, a hint-assisted answer and a fresh unassisted exercise may not belong in the same comparison. State the inclusion rule rather than discarding inconvenient attempts after looking at their times.
Incomplete attempts need a defined treatment too. A stopped clock with no correct answer should not silently become an exceptionally fast completion.
Keep the individual times beside the summary. The fastest attempt identifies one result; the mean uses every included attempt. Neither becomes a promise about the next exercise simply because it is displayed as a personal statistic.
An extra attempt changes the average differently
Add a fourth completed attempt taking 60 seconds to the original times. The total becomes 120 seconds across four attempts, so the mean becomes 30 seconds. The personal best remains 10. Reporting only the unchanged best hides the slower new attempt; reporting both measures explains why one number stayed still while the other increased.