Human Response Is Lognormal; Plan on Waiting If You Want Reliability
Thomas B. Sheridan · Ergonomics in Design The Quarterly of Human Factors Applications · 2013
Human response times fit a lognormal probability function, which poses severe constraints on the time a system designer must allow to accommodate a significant fraction of respondents; for example, 6 standard deviations for 95% confidence and 11 standard deviations for 99% confidence. When a human operates in series with machine elements, there may be no justification for demanding a quick response from the machine.