A novel method for the estimation of the background in a powder diffraction
pattern has been developed using a robust Bayesian analysis. In formulatin
g a probabilistic approach to background fitting, the diffraction peaks are
considered to be nuisance data that must be taken into account. The underl
ying probability theory is discussed in terms of going beyond the Gaussian
approximation normally associated with counting statistics and least-square
s analysis. Various examples are presented that illustrate the general appl
icability of this approach.