Insurance Selection Bias: Adverse or favorable selection bias exhibited by insurers or enrollees resulting in disproportionate enrollment of certain groups of people.Selection Bias: The introduction of error due to systematic differences in the characteristics between those selected and those not selected for a given study. In sampling bias, error is the result of failure to ensure that all members of the reference population have a known chance of selection in the sample.Insurance, Health: Insurance providing coverage of medical, surgical, or hospital care in general or for which there is no specific heading.Insurance Coverage: Generally refers to the amount of protection available and the kind of loss which would be paid for under an insurance contract with an insurer. (Slee & Slee, Health Care Terms, 2d ed)Bias (Epidemiology): Any deviation of results or inferences from the truth, or processes leading to such deviation. Bias can result from several sources: one-sided or systematic variations in measurement from the true value (systematic error); flaws in study design; deviation of inferences, interpretations, or analyses based on flawed data or data collection; etc. There is no sense of prejudice or subjectivity implied in the assessment of bias under these conditions.Selection, Genetic: Differential and non-random reproduction of different genotypes, operating to alter the gene frequencies within a population.Insurance: Coverage by contract whereby one part indemnifies or guarantees another against loss by a specified contingency.Insurance, Long-Term Care: Health insurance to provide full or partial coverage for long-term home care services or for long-term nursing care provided in a residential facility such as a nursing home.Insurance, Life: Insurance providing for payment of a stipulated sum to a designated beneficiary upon death of the insured.Insurance Carriers: Organizations which assume the financial responsibility for the risks of policyholders.Insurance Pools: An organization of insurers or reinsurers through which particular types of risk are shared or pooled. The risk of high loss by a particular insurance company is transferred to the group as a whole (the insurance pool) with premiums, losses, and expenses shared in agreed amounts.Medically Uninsured: Individuals or groups with no or inadequate health insurance coverage. Those falling into this category usually comprise three primary groups: the medically indigent (MEDICAL INDIGENCY); those whose clinical condition makes them medically uninsurable; and the working uninsured.United StatesPatient Selection: Criteria and standards used for the determination of the appropriateness of the inclusion of patients with specific conditions in proposed treatment plans and the criteria used for the inclusion of subjects in various clinical trials and other research protocols.Insurance Benefits: Payments or services provided under stated circumstances under the terms of an insurance policy. In prepayment programs, benefits are the services the programs will provide at defined locations and to the extent needed.Insurance, Dental: Insurance providing coverage for dental care.Insurance, Health, Reimbursement: Payment by a third-party payer in a sum equal to the amount expended by a health care provider or facility for health services rendered to an insured or program beneficiary. (From Facts on File Dictionary of Health Care Management, 1988)Health Benefit Plans, Employee: Health insurance plans for employees, and generally including their dependents, usually on a cost-sharing basis with the employer paying a percentage of the premium.Insurance, Liability: Insurance against loss resulting from liability for injury or damage to the persons or property of others.Insurance Claim Reporting: The design, completion, and filing of forms with the insurer.Research Design: A plan for collecting and utilizing data so that desired information can be obtained with sufficient precision or so that an hypothesis can be tested properly.Insurance, Major Medical: Insurance providing a broad range of medical services and supplies, when prescribed by a physician, whether or not the patient is hospitalized. It frequently is an extension of a basic policy and benefits will not begin until the basic policy is exhausted.Insurance, Accident: Insurance providing coverage for physical injury suffered as a result of unavoidable circumstances.Healthy Worker Effect: Phenomenon of workers' usually exhibiting overall death rates lower than those of the general population due to the fact that the severely ill and disabled are ordinarily excluded from employment.National Health Insurance, United StatesUniversal Coverage: Health insurance coverage for all persons in a state or country, rather than for some subset of the population. It may extend to the unemployed as well as to the employed; to aliens as well as to citizens; for pre-existing conditions as well as for current illnesses; for mental as well as for physical conditions.Insurance, Hospitalization: Health insurance providing benefits to cover or partly cover hospital expenses.Epidemiologic Research Design: The form and structure of analytic studies in epidemiologic and clinical research.Propensity Score: Conditional probability of exposure to a treatment given observed covariates.Health Care Reform: Innovation and improvement of the health care system by reappraisal, amendment of services, and removal of faults and abuses in providing and distributing health services to patients. It includes a re-alignment of health services and health insurance to maximum demographic elements (the unemployed, indigent, uninsured, elderly, inner cities, rural areas) with reference to coverage, hospitalization, pricing and cost containment, insurers' and employers' costs, pre-existing medical conditions, prescribed drugs, equipment, and services.Cohort Studies: Studies in which subsets of a defined population are identified. These groups may or may not be exposed to factors hypothesized to influence the probability of the occurrence of a particular disease or other outcome. Cohorts are defined populations which, as a whole, are followed in an attempt to determine distinguishing subgroup characteristics.Models, Statistical: Statistical formulations or analyses which, when applied to data and found to fit the data, are then used to verify the assumptions and parameters used in the analysis. Examples of statistical models are the linear model, binomial model, polynomial model, two-parameter model, etc.Health Insurance Portability and Accountability Act: Public Law 104-91 enacted in 1996, was designed to improve the efficiency and effectiveness of the healthcare system, protect health insurance coverage for workers and their families, and to protect individual personal health information.Medicaid: Federal program, created by Public Law 89-97, Title XIX, a 1965 amendment to the Social Security Act, administered by the states, that provides health care benefits to indigent and medically indigent persons.National Health Programs: Components of a national health care system which administer specific services, e.g., national health insurance.