JACKKNIFE A technique for estimating the variance and the bias of an estimator. If the sample size is n, the estimator is applied to each subsample of size n – 1, obtained by dropping a measurement from analysis. The sum of squared differences between each of the resulting estimates and their mean, multiplied by (n – 1)/n, is the jackknife esti- mate of variance; the difference between the mean and the original estimate, multiplied by (n – 1), is the jackknife estimate of bias.
JARGON Words and expressions used by a particular group, commonly members of a profession or trade (e.g., doctors, lawyers, astronauts, police). Derived from late Middle English iargouon, Old French, jargoun, meaning twittering of birds, incomprehensible sounds. Fowler’s Modern English Usage and Sir Ernest Gowers’s Plain Words remark adversely and at length on jargon, but perhaps the best description is Murphy’s, repro- duced in the preface of earlier editions of this dictionary: “obscure and/or pretentious language, circumlocutions, invented meanings, and pomposity delighted in for its own sake.”263 Murphy distinguishes between jargon and technical vocabulary, which expresses complex abstract thoughts with high resolution and precision, whereas jargon merely obfuscates. Medicine and its specialties, including epidemiology, are infested with jar- gon. Some can be detected in the words and phrases defined in this book. Although jargon can have legitimate uses among members of a group all of whom understand its exact meaning, it is always preferable to abide by Gowers’s admonition and use plain words whenever they are sufficiently precise.
JARMAN SCORE An index of community-wide social deprivation, used mainly by gen- eral practitioners in the United Kingdom.264 Unlike the Townsend score, the Jarman score has no theoretical basis; it uses weighted values for percentages of elderly persons living alone; children aged under 5 years; single-parent families; social class V (unskilled workers); the unemployed; overcrowded dwellings; changed address in the past year; ethnic minorities. The Jarman score correlates quite well with other indexes as a mea- sure of group socioeconomic status in administratively defined jurisdictions such as urban areas. See also Gini coefficient; overcrowding; Townsend score.
JELLINEK FORMULA A formula to estimate the prevalence of alcohol-related disease, based on the assumption that a predictable proportion of persons addicted to alcohol die of cirrhosis of the liver (confirmed by necropsy).265 The formula fails to allow for biases (e.g., in autopsy series), for the frequency of other causes of cirrhosis, and for variations in the dose response and end-organ damage produced by alcohol abuse. It is therefore flawed.
JOB EXPOSURE MATRIX (JEM) A cross-classification of jobs and occupational exposures. Some matrices are based on tasks instead of jobs. JEMs may be based on the assessment by experts of likely occupational exposures (chemical, physical, biological, and psychosocial agents) for an open or fixed list of jobs (or tasks), usually coded according to some established national or international classification system. Some JEMs also include information for different calendar time periods.266
JOB STRAIN MODELS Models to explain work-related stress based on dimensions as job demands (e.g., psychological conflicts related to work pace or workload) and job control (or job decision latitude, defined as the combination of the worker’s job deci- sion-making authority and use of skills on the job). Jobs characterized by high “psycho- logical workload demands” and low “decision latitude” increase risk for psychological job strain. Research in occupational epidemiology has shown that increased decision latitude is often preferable to reduced job demand so as to reduce mental strain. A third dimension is workplace social support (given by workmates, supervisors, employers), which may act as an effect modifier over the other two dimensions.266
JONES CRITERIA A set of clinical and laboratory findings for the diagnosis of rheumatic fever. The criteria include presence of group A hemolytic streptococcal infection; major manifestations (carditis, polyarthritis, etc.); minor manifestations (fever, arthralgia, etc.); ancillary tests (raised erythrocyte sedimentation rate, C-reactive protein, etc.).