ITR Atlas
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QWERTY Typing (Sholes & Glidden, 1874)

Measured by Dhakal, Feit, Kristensson & Oulasvirta · ACM CHI 2018 (2018)

Manual Keyboard 1874

Inputs

The measured or assumed values behind the calculations, each with its source.

rate = 51.56 wpm
Average across 168,000 participants (136M keystrokes); fastest users ~120 wpm. The system date comes from the Remington/Sholes & Glidden QWERTY typewriter; the throughput is measured in the 2018 web typing study.
P = 0.9884
1 − 1.16% average error rate (2.3 corrections per sentence)
H = 1.0 bits/char
English-text entropy (Shannon estimate).
N = 30
Distinguishable keys, used only for the raw-key Wolpaw ceiling (uniform prior over the alphabet). The headline Shannon figure instead uses English entropy, since real keystrokes are not uniform.
T_key = 0.2328 s/keystroke
Gross keystroke interval for the Wolpaw ceiling: 60 / (51.56 wpm × 5) = 0.2328 s. Gross (not error-discounted) because Wolpaw's accuracy term P handles errors separately.

Strictest ITR

Each scoring method is an upper bound on the channel, so the headline is the strictest (smallest) one for this entry. Use the score selector on the home page to view any single method across entries.

Strictest Shannon (text) Recomputed
Character-entropy throughput
Net of English redundancy and typing errors
4.25 bits/s

  1. Net words per minute

    51.56 wpm × (1 − 0.0116) = 50.96 net wpm

  2. Characters per minute

    50.96 × 5 chars/word = 254.8 chars/min

  3. Bits per character

    H(English) ≈ 1.0 bit/char (Shannon)

    English is highly redundant, so raw keystroke count would overstate information.

  4. Information transfer rate

    254.8 char/min × 1.0 bit/char ÷ 60 s/min = 4.25 bits/s

What counts as a bit depends on the action space. The number of distinguishable actions and how likely each one is are design choices of the task, not the sensing hardware. The same modality can present a fixed set of targets, a set pruned per step by a grammar or language model, or a continuous control space. Each of these changes how many actions are live and how the probability mass is spread, and therefore the information per selection. Read the action space below before comparing headline numbers across entries.

Action space

What the user can produce at each step, and how those options are distributed.

Structure
Fixed set of targets
Size
30 distinguishable actions
Prior
Context-conditioned: likelihoods depend on prior actions
Notes
~30 keys, but the ITR uses English character entropy (~1 bit/char), a context-conditioned source, rather than the ~5 bits a uniform keystroke would carry. This bakes in the language's redundancy, so it is not directly comparable to the uniform-prior speller figures.

Comparability The strictest bound here is the Shannon entropy of the output text, under one predictor held constant across the whole atlas (≈1 bit per character). That shared predictor makes it directly comparable to every other text entry (keyboards, spellers, silent speech and speech BCIs) regardless of prior or vocabulary size. For most text interfaces it comes out tighter than the raw-selection bounds, but not always. Where a small vocabulary makes Wolpaw tighter, that wins instead. Any Fitts, Wolpaw or log₂(N) figure shown below is another bound on the same channel. Switch the home-page score selector to compare one across entries.

Other bounds considered for the headline

Also valid upper bounds for this entry and eligible to be the headline. They just came out looser than the strictest above. Pick any of these in the home-page score selector.

Wolpaw Recomputed
Wolpaw bitrate over the raw key set
Uniform-prior ceiling on the physical key channel, before English redundancy
20 bits/s

  1. Bits per selection (Wolpaw formula)

    B = log2(N) + P*log2(P) + (1-P)*log2((1-P)/(N-1))
  = log2(30) + 0.9884*log2(0.9884) + 0.0116*log2(0.0116/29)
  = 4.759 bits / selection

    Term 1 is the information if every choice were correct; terms 2-3 subtract the bits lost to the error rate, assumed spread evenly over the other N-1 targets.

  2. Selections per second

    T = 0.2328 s/selection  ->  1 / 0.2328 = 4.296 selections/s

  3. Information transfer rate

    ITR = B * selections/s = 4.759 * 4.296 = 20.444 bits/s

Other score types

Bounds the atlas keeps out of the default strictest headline: as-reported figures, alternate task conditions, or raw-channel ceilings that shouldn't win the headline by default. Each still carries a score type, so the home-page selector ranks this entry on it when you choose that type. Read its derivation before comparing across entries.

Nuyujukian Recomputed
Nuyujukian achieved bitrate over the raw key set
Achieved-bitrate view of the key channel, shown for comparison
20 bits/s

  1. Achieved-bitrate credit per net-correct key

    N = 30 keys → log2(N − 1) = log2(29) = 4.86 bits per net-correct selection (field-standard achieved bitrate, e.g. Webgrid; Nuyujukian 2015, which introduced the metric, used log2(N)).

  2. Net-correct key rate

    net-correct = 2P − 1 = 2(0.9884) − 1 = 0.977 of keys. At 0.2328 s/key → 0.977 / 0.2328 = 4.20 correct/s.

    A typing error commits the wrong character rather than timing out, so incorrect = 1 − P. Same N (30 keys), accuracy (98.84%) and keystroke interval (0.2328 s) as the entry's raw-key Wolpaw ceiling, and lands on the same ~20 bits/s. Both are the uniform-prior key channel before English redundancy, far above the 4.25 bits/s Shannon headline that holds this entry to the realized text.

  3. Achieved bitrate

    4.86 bits × 4.20 correct/s = 20.4 bits/s.

Source

Authors
Dhakal, Feit, Kristensson & Oulasvirta
Publication
ACM CHI 2018, 2018
Paper
10.1145/3173574.3174220
Reference
System date: Smithsonian NMAH on the Remington/Sholes & Glidden QWERTY typewriter