Understanding Percentile Ranks
Percentiles divide a distribution into 100 equal parts. The 50th percentile (median) splits the population in half. Unlike raw scores, percentiles immediately communicate relative standing - a reaction time at the 90th percentile means you responded faster than 90% of test-takers. Percentiles are non-linear; the difference between the 50th and 60th percentile in raw score is typically smaller than between the 90th and 95th.
Percentiles vs. Other Metrics
Percentiles differ from percentages (which measure proportion correct) and from standard scores like z-scores or IQ scales. While z-scores assume normal distribution and allow arithmetic operations, percentiles work with any distribution shape and are more intuitive for general audiences. However, percentiles cannot be averaged or directly compared across different tests without shared norms.
Percentiles in Cognitive Benchmarking
Benchmark platforms use percentiles to contextualize individual results against population norms. Your reaction time of 215 ms gains meaning when expressed as the 72nd percentile. Reference populations matter - percentiles calculated against all users differ from those restricted by age group or experience level. Larger sample sizes produce more stable and reliable percentile estimates.