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# 14.6 Probability and magnitude of continuous effects

Equations (2) and (4) require two types of input for continuous effects: first, a dose-response relationship describing the magnitude of the effect, and secondly, the probability that the effect will occur (i.e. begin) in the current year, as a function of age. All of the issues discussed above for quantal effects apply in similar ways to one or both of these two parameters: the effect may be chronic or acute, may depend on covariates which must be expressed in discrete form, probabilities must relate to onset in the current year, and both probability and magnitude must be expressed in absolute not relative terms and relate to occurrence of the effect in humans (extrapolated if necessary from animals).

The probability and magnitude of effect may both be functions of the same measure of intake and therefore correlated with one another. This can be represented in the Qalibra software by specifying both as functions of the same measure of intake, and using the same intake data.

The Qalibra software uses linear interpolation between points specified by the user to construct continuous dose-response relationships for both probability and magnitude of effect (as for the probability of quantal effects, see section 14.5). Alternatively, a single value can be used to represent a threshold for probability of effect (with the same restriction as for quantal effects), but not for magnitude of effect.