UICC Union Internationale Contre le Cancer (International Union Against Cancer) (www.uicc.org).

UIP Universal Immunisation Program (www.who.int/immunization).

UN United Nations (www.un.org).

UNAIDS Joint United Nations Programme on HIV/AIDS (www.unaids.org).

UNBIASED ESTIMATOR An estimator that, for all sample sizes, has an expected value equal to the parameter being estimated. If an estimator tends to be unbiased as sample size increases, it is referred to as asymptotically unbiased.

UNDERLYING CAUSE OF DEATH The disease or injury that initiated the train of events leading directly to death, or the circumstances of the accident or violence that produced the fatal injury. See death certificate.

UNDERREPORTING Failure to identify and/or count all cases, leading to reduction of the numerator in a rate. See also error.

UNDP United Nations Development Programme (www.undp.org).

UNEP United Nations Environmental Programme (www.unep.org).

UNFPA United Nations Population Fund (www.unfpa.org).

UNHCR United Nations High Commission for Refugees (www.unhcr.org).

UNICEF United Nations Children’s Fund (www.unicef.org).

UNIVERSAL PRECAUTIONS Procedures to be followed when health workers anticipate the possibility of infection by a patient who may harbor a highly contagious, dangerous pathogen. Universal precautions may include segregation of the patient in a private room; use of gloves, gown, mask, Perspex shield (eye protection); and rigorous attention to ensuring that no blood or other body fluid from such a patient can come into contact with the skin or mucous membranes of the health care worker. See also needle stick and barrier nursing.

UNIVERSE, UNIVERSE POPULATION The entire population from which a sample is selected for study. The term is seldom used and is preferably avoided outside of theo- retical discussions.

UNMEASURED CONFOUNDING See residual confounding.

UNOBTRUSIVE MEASURES A set of methods for assessing behavior without actually asking people how they behave or examining them physically to determine the effects of their behavior.386

USPHS United States Public Health Service (www.usphs.gov).

UTILITY The value of a particular health state, usually expressed on a scale from 0 to 1; it is used in defining quality-adjusted life years (QALYs) and health-adjusted life expectancy. Utility is determined from preferences expressed by an individuals in a Von Neumann–Morgenstern standard gamble, time trade-off, or other related technique. See also cost-utility analysis.

UTILITY-BASED UNITS In the context of quality-adjusted life years (QALYs), utility- based units relate to a person’s level of well-being estimated on the basis of the total life years gained from a procedure or intervention.

UTILITY, CLINICAL Risks and benefits associated with the introduction of a screening or diagnostic test into clinical practice.14,62,193,210–213,355,387 See also significance, clinical.