The interaction of two binary variables, assumed to be empirical
observations, has three degrees of freedom when expressed as a matrix of
frequencies. Usually, the size of causal influence of one variable on the other
is calculated as a single value, as increase in recovery rate for a medical
treatment, for example. We examine what is lost in this simplification, and
propose using two interface constants to represent positive and negative
implications separately. Given certain assumptions about non-causal outcomes,
the set of resulting epistemologies is a continuum. We derive a variety of
particular measures and contrast them with the one-dimensional index.Comment: 20 pages, 3 figure