All articles starting with F

Functional family therapy

Functional family therapy (FFT) is a short-term, family-based treatment for adolescents with behavioral problems such as delinquency and substance use, developed at the University of Utah in 1969.

Oct 15, 2026

A functional feeding group (FFG) is a classification of aquatic macroinvertebrates by their food-acquisition mechanism rather than taxonomy, proposed by Kenneth W. Cummins in 1973 with groups including shredders, collectors, scrapers, and predators.

Functional Food

Functional food: foods offering health benefits beyond basic nutrition, also called nutraceuticals or designer foods. No legal definition in EU or US; concept from Japan's 1984 project and FOSHU system; regulated via health-claim frameworks.

Functional gallbladder disorder

Functional gallbladder disorder, also called biliary dyskinesia or chronic acalculous cholecystitis, is biliary pain without gallstones or structural pathology, diagnosed by Rome IV criteria and HIDA ejection fraction, and often treated with cholecystectomy of uncertain benefit.

Functional gastrointestinal disorder

Functional gastrointestinal disorder (FGID), now disorders of gut-brain interaction (DGBI), chronic GI symptom syndromes diagnosed by Rome criteria; over 40% global prevalence, renamed by Rome IV 2016, Rome V 2026.

Functional group

A functional group is an atom or group of atoms whose characteristic chemistry defines families of organic compounds largely regardless of size, sitting on a molecule's unreactive backbone.

Functional group interconversion

Functional group interconversion (FGI) is the conversion of one functional group of an organic molecule into another by substitution, addition, elimination, oxidation, or reduction, keeping the carbon skeleton intact.

Functional heartburn

Functional heartburn (FH): retrosternal burning with normal acid exposure, endoscopy, and manometry, a Rome IV gut-brain disorder distinct from GERD and reflux hypersensitivity; PPIs fail, neuromodulators help.

Functional illiteracy

Functional illiteracy, or being functionally illiterate, is when reading and writing skills fall short of what daily life and work require, though a person can decode simple text.

Functional Independence Measure

The Functional Independence Measure (FIM) is an 18-item rating scale used in rehabilitation medicine to quantify the assistance a person with a disability needs for daily activities.

Functional integration (formal methods)

Functional integration in formal methods is a program-development technique in which specification, implementation, and correctness proof are produced together, so the delivered program is correct a priori.

Functional linguistics

Functional linguistics explains language structure through communicative function and use, spanning the Prague School (founded 1926 by Mathesius), Halliday's Systemic Functional Linguistics, Dik's Functional Grammar, and RRG, in contrast to formal explanation.

Functional lumen imaging probe

The functional lumen imaging probe (FLIP), marketed as EndoFLIP, is an endoscopic catheter that measures luminal distensibility during balloon distention, used to assess the esophagogastric junction and pylorus.

Functional luminal imaging

Functional luminal imaging (FLIP) is an endoscopic technique that measures the size and compliance of a distended gastrointestinal lumen by impedance planimetry, used mainly to assess the esophagogastric junction in motility and reflux disease.

Functional magnetic resonance imaging

Functional magnetic resonance imaging (fMRI), including BOLD task fMRI and resting-state fMRI, noninvasively maps brain activity via blood oxygenation; developed from Ogawa's 1990 BOLD discovery, used clinically for presurgical planning, with known poor task-fMRI test-retest reliability (mean ICC .397).

Functional medicine

Functional medicine: a root-cause, systems biology care model from Jeffrey Bland and the Institute for Functional Medicine (IFM), featuring extended history-taking, nonstandard lab panels, supplement protocols, certification (FMCP-M), mixed evidence, and direct-pay costs.

Functional near-infrared spectroscopy

Functional near-infrared spectroscopy (fNIRS), also called optical topography or diffuse optical imaging, is a portable, non-invasive neuroimaging method using 650–950 nm light to measure cortical HbO/HbR hemodynamic changes; first human studies 1991/1992, standardized by IEC 80601-2-71:2025.

Functional neuroimaging

Functional neuroimaging measures human brain activity via fMRI, PET, MEG, EEG, and fNIRS, either hemodynamically (millimeter spatial, seconds temporal) or electromagnetically (millisecond temporal), with clinical use in presurgical brain mapping.

Functional Orthodontic Appliances

Functional orthodontic appliances (activator, Herbst, Twin Block, Frankel regulator) are removable or fixed devices that correct Class II malocclusion by posturing the mandible forward, using muscle forces to modify jaw growth in children.

Functional parkinsonism

Functional parkinsonism (FP), ICD-11 8A00.3, is a parkinsonian syndrome caused by functional neurological disorder, not dopamine degeneration; tremor, rigidity, and slowness show distractibility, entrainment, and no true bradykinesia.

Oct 15, 2026

Functional principal component analysis

Functional principal component analysis (FPCA) extends principal component analysis to curves, surfaces, and other functions, and is the most widely used technique in functional data analysis.

Functional programming

Functional programming is a declarative style of programming that treats computation as evaluating mathematical functions, favoring pure functions and immutable data, with languages including LISP, ML, and Haskell.

Functional reach test

The functional reach test is a clinical balance assessment that measures the difference between arm's length and maximal forward reach with feet fixed, screening postural stability and fall risk.

Functional regression

Functional regression, also known as functional linear regression, is a family of statistical regression methods where predictors or responses are curves, applied to data like imaging and accelerometry.

Functional renormalization group

The functional renormalization group (FRG) is a nonperturbative method in quantum field theory and statistical physics that describes how the effective action changes with an energy or momentum scale.

Functional renormalization of gravity

Functional renormalization of gravity applies the functional renormalization group, via Wetterich's effective average action, to quantum gravity, where a non-Gaussian fixed point suggests gravity is asymptotically safe.

Functional requirement

A functional requirement states what a system must do, expressed as an obligation on the product rather than how it will be built, and is typically written as a "shall" statement.

Functional Residual Capacity

Functional residual capacity (FRC): lung gas volume after normal passive exhalation, ERV plus RV, about 3 L normally. Measured by plethysmography, helium dilution, or nitrogen washout, not spirometry; rises in obstruction, falls in obesity and anesthesia.

Functional resonance analysis method

The functional resonance analysis method (FRAM) is a qualitative safety analysis technique by Erik Hollnagel that models how everyday performance variability can resonate into accidents.