Mack―Wolfe test: A distribution-free method for one-way designs used to test a null hypothesis of equality of treatment effects against an alternative specifying an umbrella ordering. [Hollander, M. andWolfe, D. A., 1999, Nonparametric Statistical Methods, J. Wiley & Sons, New York.]

Mahalanobis D2: A measure of the distance between two populations or two samples of individuals based on observations on a number of variables measured on each. The measure is based on the difference of the mean vectors of each group and on their assumed common variance―covariance matrix. See also Hotelling's T test. [Everitt, B. S. and Dunn, G., 2001, Applied Multivariate Data Analysis, 2nd edn, Arnold, London.]

Main effect: An estimate of the independent effect of (usually) a factor variable on a response variable in analysis of variance.

Mainframe: High-speed, general-purpose computer with a very large storage capacity.

Majority rule: A requirement that the majority of a series of diagnostic tests are positive before declaring that a patient has a particular complaint. See also unanimity rule.

Malthusian parameter: The rate of increase that a population would ultimately attain if its age-specific birth rate and age-specific death rate were to continue indefinitely. See also population growth model. [Proceedings of the National Academy of Sciences of the United States of America, 1996, 93, 15276–8.]

Management trial: Synonymous with pragmatic trial. Manifest variable: A variable that can be measured directly, in contrast to a latent variable. For example, blood pressure, weight, height, etc.