Basic Error Rates

This page describes human error rates in a variety of contexts.

Most of the error rates are for mechanical errors. A good general figure for mechanical error rates appears to be about 0.5%.

Of course the denominator differs across studies. However only fairly simple actions are used in the denominator.

The Klemmer and Snyder study shows that much lower error rates are possible--in this case for people whose job consisted almost entirely of data entry.

The error rate for more complex logic errors is about 5%, based primarily on data on other pages, especially the program development page.

 
 

Study

Detail

Error Rate

Baddeley & Longman [1973]

Entering mail codes. Errors after correction. Per mail code.

0.5%

Chedru & Geschwind [1972]

Grammatical errors per word

1.1%

Dhillon [1986]

Reading a gauge incorrectly. Per read.

0.5%

Dremen and Berry [1995]

Percentage error in security analysts' earnings forecasts for reporting earnings. 1980 / 1985 / 1990. That is, size of error rather than frequency of error.

30%

52%
65%

Edmondson [1996]

Errors per medication in hospital, based on data presented in the paper. Per dose.

1.6%

Grudin [1983]

Error rate per keystroke for six expert typists. Told not to correct errors, although some did. Per keystroke.

1%

Hotopf [1980]

S sample (speech errors). Per word

0.2%

Hotopf [1980]

W sample (written exam). Per word

0.9%

Hotopf [1980]

10 undergraduates write for 30 minutes, grammatical and spelling errors per word

1.6%

Klemmer [1962]

Keypunch machine operators, errors per character

0.02% to 0.06%

Klemmer [1962]

Bank machine operators, errors per check

0.03%

Kukich [1992]

Nonword spelling errors in uses of telecommunication devices for the deaf. 40,000 words (strings). Per string.

6%

Mathias, MacKenzie & Buxton [1996]

10 touch typists averaging 58 words per minute. No error correction. In last session. Per keystroke.

4%

Mattson & Baars [1992]

Typing study with secretaries and clerks. Nonsense words. Per nonsense word.

7.4%

Melchers & Harrington [1982]

Students performing calculator tasks and table lookup tasks. Per multipart calculation. Per table lookup. Etc.

1%-2%

Mitton [1987]

Study of 170,016 errors in high-school essays, spelling errors. Per word. 

2.4%

Potter [1995]

Errors in making entries in an aircraft flight management system. Per keystroke. Higher if heavy workload.

10.0%

Rabbit [1990]

Flash one of two letters on display screen. Subject hits one of two keys in response. After correction. Per choice.

0.6%

Schoonard & Boies [1975]

Line-oriented text editor. Error rate per word. Without correction /  with error correction.

3.4% / 0.52%

Shaffer & Hardwick [1968]

Residual typing errors per character. Subjects with error rates higher than 2.5% were excluded. All qualified touch typists, including excluded. 20 subjects finally used.

0.63%

Swain & Guttman [1983]

Interpreting indicator on an indicator lamp. Per interpretation.

0.1%

Swain & Guttman [1983]

Error reading an analog meter. Per read.

0.3%

Swain & Guttman [1983]

Choosing an incorrect panel control control from a number of similar controls. Per choice.

0.3%

Swain & Guttman [1983]

Error reading chart recorder. Per read.

0.6%

Swain & Guttman [1983]

Error reading a graph. Per read.

1%

Swain & Guttman [1983]

Turning control in wrong direction under extreme stress. Per turn.

50%

Tsao [1990]

Nonword spelling errors in uses of TDD (telecommunication devices for the deaf) 130,000 strings. Per string.

5%

Van Nes [1971]

Hand-written text, grammatical errors. Per word assuming 5 letters per word

0.3%-3.0%

Wing & Baddeley [1980]

Grammatical errors in examination at Cambridge. Per word.

0.5%

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