Presents the results of a review of numerical modelling stiffness and strength properties used to simulate rock masses. Papers where laboratory and modelling properties are given have been selected from the mass of more general modelling literature. More specifically papers that have reduced stiffness and/or strength parameters from laboratory to field values have been targeted. The result of the search has been surprising: of the thousands of papers on numerical modelling, a few hundred mention laboratory and rock mass properties, and of those, only some 40 appear to apply some kind of reduction. The papers that apply a reduction have been used to produce the graphs that constitute the main content of this paper. Rock stiffness properties have been separated from those of strength in the analysis and this has illustrated interesting differences in their respective average reduction factors.; Reduction factor is applied to rock properties found from laboratory testing for the data to be applied in numerical modelling. The data were extracted from 44 separate works. It was found that strength and stiffness properties are needed to be treated separately when examining the effect of the rock mass upon them. Strength is best modeled either by the Trueman approach or by Hoek and Brown's more complex approach for a better failure envelope. However, in the case of low strength, stiffness, or RMR these approaches are unsatisfactory. The modeled rock mass property values are not necessarily measured and in some cases simply the opinion of the particular engineer.
