Glossary

Search results

Accessibility Metric(also: Web Accessibility Metric, Accessibility Score)

A quantitative measure used to assess and compare the accessibility quality of web pages or websites. Accessibility metrics typically calculate a score (often 0-100%) based on the number and severity of WCAG violations found, weighted by conformance level (Level A weighted…

Accessibility Metric(also: Web Accessibility Metric, Accessibility Quality Metric)

An accessibility metric is a quantitative measure used to assess the level of accessibility compliance of a web page or website. Metrics typically derive from the results of automated or manual evaluation of WCAG checkpoints, aggregating pass/fail/warning outcomes into a single…

Accessibility Progress Formula(also: APPF, Accessibility Progress Percentage)

A formula for quantitatively tracking progress in addressing accessibility issues on a website, expressed as APPF = A / ((A + B) + (T - C)), where A is the number of applicable checklist items that have been addressed, B is the number not yet addressed, T is the total number of…

Barrier Impact Factor(also: BIF, Accessibility Barrier Impact)

A metric for measuring the severity of web accessibility barriers by weighting detected errors according to which assistive technologies and disability groups they affect. The BIF is calculated by summing the product of the number of errors and a weight value for each affected…

Character Error Rate(also: CER)

A metric for evaluating automatic speech recognition (ASR) and optical character recognition (OCR) accuracy, measuring the minimum number of character-level edits (insertions, deletions, substitutions) needed to transform the system output into the reference text, divided by the…

Communication Rate(also: Communication Speed)

The speed at which a person can convey messages, typically measured in words per minute (WPM). For AAC users, communication rate is often significantly slower than natural speech (100-200 WPM)—unaided AAC users may achieve only 2-10 WPM with scanning systems, while more advanced…

Correctness(also: Precision, Validity)

In the context of accessibility evaluation, correctness (also called precision) is the proportion of reported accessibility problems that are true problems — that is, issues that genuinely affect users with disabilities rather than false positives. A high correctness rate means…

Dale-Chall Readability Formula(also: Dale-Chall, New Dale-Chall)

A readability formula first published by Edgar Dale and Jeanne Chall in 1948 and revised in 1995. Unlike formulas that rely only on surface counts, Dale-Chall compares every word in a text against a manually curated list of "easy" words familiar to fourth-grade readers; the raw…

Equal Error Rate(also: EER, Crossover Error Rate)

A metric used to evaluate biometric system performance, representing the point at which the false acceptance rate (wrongly accepting unauthorized users) equals the false rejection rate (wrongly rejecting authorized users). Lower EER values indicate better system accuracy. In…

Evaluation Reliability(also: Inter-rater Reliability, Evaluator Agreement)

The extent to which independent accessibility evaluations of the same content produce consistent results. High reliability means that different evaluators using the same method will identify similar sets of accessibility problems, while low reliability indicates that results…

F-measure(also: F-score, F1 Score)

A metric that combines correctness (precision) and sensitivity (recall) into a single balanced score, calculated as the harmonic mean of the two values. In accessibility evaluation research, the F-measure provides a single number representing the overall effectiveness of an…

Gunning Fog Index(also: Gunning FOG, FOG Index)

A traditional readability formula developed by Robert Gunning in 1952 that estimates the years of formal education a reader needs to understand a text on first reading. It is calculated from average sentence length plus the percentage of "complex" words — words with three or…

Input Rate(also: Keystroke Rate)

The speed at which a user can produce individual keystrokes or character inputs, typically measured in seconds per keystroke. Input rate varies dramatically across access methods: touch typists may achieve 0.1-0.2 seconds per keystroke, while users of switch scanning systems or…

Keystroke Saving(also: KS, Keystroke Reduction)

A metric used to evaluate word prediction and word completion systems, measuring the percentage of keystrokes that a user can avoid by accepting system predictions instead of typing each character individually. Keystroke saving is calculated by comparing the number of keystrokes…

Keystroke Saving Rate(also: KSR, Keystroke Savings)

A metric measuring the efficiency of text prediction systems by calculating the percentage of keystrokes saved compared to typing the same text on a standard keyboard without prediction. A KSR of 50% means the user needed only half the keystrokes they would have required…

Keystroke Savings(also: KS, Key Savings)

A metric used to evaluate word prediction systems, measuring the percentage of keystrokes eliminated by accepting predictions compared to typing the full text character by character. While keystroke savings is commonly reported in AAC research, it does not directly translate to…

Keystrokes Per Character(also: KSPC)

A metric used to evaluate the efficiency of text-entry methods by measuring the average number of keystrokes required to produce each character of text. A lower KSPC indicates a more efficient input method. For standard MultiTap on a 12-key phone keypad, the theoretical best…

Lexile Framework(also: Lexile, Lexile Measure)

A commercial readability framework developed by MetaMetrics that places both texts and readers on a common scale — the Lexile measure — to support matching readers with materials at an appropriate level of challenge. A text's Lexile measure is computed from sentence length and…

LogMAR(also: Logarithm of the Minimum Angle of Resolution)

A standardised scale for measuring visual acuity based on the logarithm (base 10) of the minimum angle of resolution, used in the Bailey-Lovie eye chart and widely adopted in clinical vision research. A logMAR value of 0.0 corresponds to 20/20 (6/6) vision, with higher values…

Minimum String Distance(also: MSD, Edit Distance, Levenshtein Distance)

A metric for measuring text entry accuracy by calculating the minimum number of single-character insertions, deletions, and substitutions needed to transform the transcribed text into the intended text. In text entry research, the MSD error rate is typically expressed as a…

Perplexity(also: Language Model Perplexity)

A standard metric for evaluating language models that measures how well the model predicts a sample of text. Mathematically, perplexity is the inverse probability of the test set, normalised by the number of words — a lower perplexity indicates that the model assigns higher…

Prediction Utilization(also: PU)

The percentage of opportunities where a user accepts a word prediction rather than continuing to type the word manually. Prediction utilization reflects user trust in a prediction system—higher quality predictions lead to higher utilization rates. Research shows that users…

Reaching Time(also: Navigation Time, Time to Target)

A usability metric measuring the time required for a user to navigate to a specific element on a web page. For blind users employing screen readers, reaching time is a key indicator of page navigability and efficiency, as it captures the cumulative cost of navigating through and…

Response Time(also: Reaction Time, Tact)

The time elapsed between the presentation of a stimulus and the user's physical response, typically measured in milliseconds. In scanning-based AAC, response time (often called Tact) is the interval between when an item is highlighted and when the user activates the switch.…

SMOG(also: SMOG Index, SMOG Grade, Simple Measure of Gobbledygook)

A readability formula developed by G. Harry McLaughlin in 1969 that estimates the years of education needed to understand a text, based on the number of polysyllabic words (three or more syllables) in a fixed sample of sentences. SMOG is widely used in healthcare communication…

Sensitivity(also: Recall, Thoroughness, Completeness)

In the context of accessibility evaluation, sensitivity (also called recall or thoroughness) is the proportion of true accessibility problems that are successfully identified and reported by an evaluator. High sensitivity means that most real barriers are found, while low…

Text Entry Rate(also: Typing Speed, Characters Per Minute, CPM)

A measure of how quickly a user can input text using a given method, typically expressed in words per minute (WPM) or characters per minute (CPM). One word is conventionally defined as five characters including spaces. For standard QWERTY keyboards, professional typists achieve…

Text Generation Rate(also: TGR, Text Entry Rate, Text Entry Speed)

The speed at which a user produces text, typically measured in words per minute (WPM) or characters per second. Text generation rate is a key performance metric in assistive technology evaluation because it captures the overall efficiency of a text entry system, accounting for…

Throughput(also: Throughput (Fitts), Pointing Throughput)

In human-computer interaction, throughput is a combined speed-accuracy metric derived from Fitts's law that measures the efficiency of aimed pointing movements, expressed in bits per second (bps). It is calculated by dividing the index of difficulty (a function of target…

Unified Web Evaluation Methodology(also: UWEM)

A standardized methodology developed by the European Web Accessibility Benchmarking Cluster (WAB Cluster) for evaluating the accessibility of websites in a consistent, comparable way. UWEM provides formulas for calculating quantitative accessibility scores from WCAG checkpoint…

Violation Score(also: Accessibility Score, A11y Score)

A numerical metric used to quantify the severity and prevalence of accessibility violations on a web page or within a dataset. Violation scores typically map qualitative impact levels (cosmetic, minor, moderate, serious, critical) to numerical values, enabling quantitative…

Visual acuity(also: VA, LogMAR acuity, Snellen acuity)

A measure of the sharpness or clarity of vision, typically expressed as a Snellen fraction (e.g., 20/20, 20/200) or LogMAR value. A person with 20/200 vision must be 20 feet away to see what someone with normal vision sees at 200 feet. Visual acuity of 20/200 or worse in the…

Web Accessibility Barrier(also: WAB, Accessibility Barrier)

Any element, design pattern, or technical implementation on a web page that prevents or hinders people with disabilities from accessing, understanding, or interacting with content. Common web accessibility barriers include images without alternative text, videos without…

Web Accessibility Barrier Score(also: WAB, WAB Score)

A quantitative metric for measuring the accessibility level of a website, defined as the mean value of the failure rate of accessibility checkpoints on a page, weighted by the priority of each checkpoint. The failure rate is the number of violations of a checkpoint divided by…

Web Accessibility Quantitative Metric(also: WAQM)

An accessibility evaluation metric that calculates a quantitative score for a website based on automatically generated evaluation reports. WAQM computes the failure rate for each tested page, then derives the overall website accessibility value by weighting pages according to…

Web Complexity(also: Page Complexity, Website Complexity)

A measure of the technical sophistication and structural density of a web page, typically assessed by the number and types of HTML elements, scripts, embedded objects, and interactive features present. In accessibility research, web complexity is an important factor because more…

Web Page Complexity(also: Page Complexity, Structural Complexity)

A measure of how much a web page contains in terms of interactivity, embedded media, and structural richness. The W3C's WCAG-EM defines complexity through three factors: level of interactivity, source and method of content generation, and implementation style. Quantitative…

Word Error Rate(also: WER)

A metric used to evaluate the accuracy of automatic speech recognition (ASR) and captioning systems, calculated as the number of word-level errors (insertions, deletions, and substitutions) divided by the total number of words in the reference transcript. Lower WER indicates…

Word error rate(also: WER)

The standard metric for evaluating automatic speech recognition accuracy, calculated as the number of substitutions, deletions, and insertions divided by the total number of words in the reference transcript. Research with DHH users has shown that WER correlates poorly with…

Words Per Minute(also: WPM)

A standard measure of speech or reading speed, representing the number of words produced or comprehended in one minute. Typical human speech occurs at 120-180 WPM, average reading speed is 200-250 WPM, while experienced screen reader users can comprehend synthesized speech at…

40 results.