  To investigate the relation between observations of the 10.7 cm flux and the
international sunspot number so that a physical unit may be ascribed to
historical records, both polynomial and power law models are developed giving
the radio flux as a function of sunspot number and vice versa. Bayesian data
analysis is used to estimate the model parameters and to discriminate between
the models. The effect on the parameter uncertainty and on the relative
evidence of normalizing the measure of fit is investigated. The power law
giving flux as a function of sunspot number is found to be the most plausible
model and may be used to estimate the radio flux from historical sunspot
observations.
