The article discusses the development of a method for relating reactivity to crystallite size and strain parameters obtained by the Warren-Averbach technique. EPA has been using crystallite size and strain data obtained from x-ray diffraction (XRD) peak profile analysis to predict the reactivity of solid calcium hydroxide sorbent with acid gases in combustion streams. The software used for the calculations requires that the XRD peak profile be corrected with a distribution function before application in the Warren-Averbach analysis. The curve-fitting software, available on the system, includes the Gaussian, Lorentzian, pseudo-Voight, Pearson VII, and Split Pearson VII distribution functions. The function parameters are specified roughly at the start, and the computer algorithm then optimizes the fit parameters by the least squares method. Most of the work has been on calcium hydroxide sorbent materials with calcium fluoride as a standard to account for instrument effects on the peaks. It has been observed that none of the functions produce a satisfactory fit for the experimental XRD peaks.