WONCA International Classification Committee

UNDER-REPORTING

Failure to identify and/or count all cases, leading to reduction of numerator in a rate.

URBAN PRACTICE POPULATION

See POPULATION, PRACTICE.

VALIDATION

The process of establishing that a method is sound.

VALIDITY, STUDY

The degree to which the inference drawn from a study, especially generalisations extending beyond the study sample, are warranted when account is taken of the study methods, the representativeness of the study sample, and the nature of the population from which it is drawn.

VALIDITY, TEST

The extent to which a particular instrument measures what it is intended to measure and does not measure what it is not supposed to. Can be divided into several subgroupings :
1. Concurrent validity : a form of validity in which the measure being tested and the comparison measure are administered at the same point in time.
2. Construct validity : a process in which validity is evaluated as the extent to which a measure correlates with variables in a manner consistent with theory.
3. Content validity : the extent to which a measure or battery represents the universe of measurements, objects or domains, avoiding over-emphasis of some and under-emphasis of others.
4. Convergent validity : the strength of association between two methods of measuring the same construct.
5. Criterion validity : the extent to which a measure corresponds to an accurate or previously validated measure of the same concept.
6. External validity : Able to generalize results.
7. Face validity : the extent to which a measure "looks like" what it is intended to measure.
8. Internal validity : refers to the degree of confidence in the conclusions drawn in relation to the research methods used.
9. Predictive validity : test performance related to subsequent performance in practice.

VARIABILITY

The extent to which all possible scale levels are observed.

VARIABLE

Any quantity which changes. A variable can be an attribute, a phenomenon or an event which characterizes an object. Variable can be dependent or independent.
1. Dependent variable : a characteristic being observed or measured that is hypothesised to influence an event or manifestation within a defined area of relationships under study.
2. Independent variable : not influenced by the event or manifestation but may cause or contribute towards its variation (See JM Last : A Dictionary of Epidemiology).

VARIANCE

A measure of the variation shown by a set of observations, defined by the sum of the squares of deviations from the mean divided by the number of degrees of freedom in the set of observations.

VISUAL ANALOGUE SCALE

A method for obtaining a response to a question by getting the respondent mark a labelled line to reflect the psychological distance from the endpoints.

VOCABULARY

A set of defined terms from a discipline.

VISIT

See ENCOUNTER.

VITAL STATISTICS

Systematically tabulated information concerning births, marriages, divorces and deaths based on registrations of these vital events.

WELL-BEING

The individual's subjective state of mind with regard to the bodily and emotional feelings.

WHO

World Health Organisation.

WILCOXON RANK SUM TEST

A non-parametric test which determines whether two independent samples have been drawn from the same population or from two different populations.

WONCA

World Organisation of National Colleges, Academies and Academic Associations of General Practitioners/Family Physicians now shortened to World Organisations of General/Family Practitioners.

YATES' CORRECTION

An adjustment proposed by Yates (1934) in the chi-square calculation for a 2x2 table, which brings the distribution based on discontinuous frequencies closer to the continuous chi-square distribution form which the published tables for testing chi-squares are derived.

YIELD

The number or the proportion of cases of a condition accurately identified by a screening test.