A hypothesis concerning the parameter(s) of a distribution. For example, the hypothesis that the mean of a population equals the mean of a second population, when the populations are each assumed to have a normal distribution.

Information processing involving a large number of units working contemporaneously in parallel with units, like the neurons of the brain, exciting or inhibiting one another.

A simple but powerful technique for obtaining a graphical display of multivariate data. In this plot, the variable axes are arranged horizontally, each parallel to the one above it. A line is then plotted for each observation by joining the appropriate variable values on these axes.

A study in which a group of people, the ‘panel’, are interviewed or surveyed with respect to some topic of interest on more than one occasion.

Two samples of observations with the characteristic feature that each observation in one sample has one and only one matching observation in the other sample.

Data arising when an investigator records whether a particular character istic is present or absent at two sites on the same individual.

A design which can reduce selection bias in situations where it is not possible to use random allocation of subjects to treatments.

A model with more parameters than observations for estimation.

A term applied to studies involving matching when the matching variable is strongly related to exposure but not to disease risk. Such a situation leads to a loss of efficiency.

Models that contain more unknown parameters than can be justified by the data.