IBD: Abbreviation for identical by descent.

ICD: Abbreviation for international classification of disease.

IDA: Abbreviation for initial data analysis.

Identical by descent: A term used when two genes at a given locus have both been inherited from a common ancestor. For example, in a family without inbreeding, two siblings who have inherited the same gene from their father but two different genes from their mother have one gene (the paternal one) to which the term applies. [American Journal of Human Genetics, 1990, 47, 842–53.]

Identification: The degree to which there is sufficient information in the sample observations to estimate the parameters in a proposed model. An unidentified model is one in which there are too many parameters in relation to the number of observations to make estimation possible. A just identified model corresponds to a saturated model. Finally, an overidentified modelis one in which parameters can be estimated and there remain some degrees of freedom to allow the fit of the model to be assessed.

Immigration–emigration models: Models for the development of a population that is augmented by the arrival of individuals who found families independent of each other. [Jagers, P., 1975, Branching Processes with Biological Applications, J. Wiley & Sons, New York.]

Immune proportion: The proportion of individuals who may not be subject to death, failure, relapse, etc. in a sample of censored survival times. The presence of such individuals may be indicated by a relatively high number of individuals with large censored survival times.