"The Site Index – Biogeoclimatic Ecosystem Classification (SIBEC) model allows site index, which is a measure of site productivity, to be estimated from Biogeoclimatic Ecosystem Classification site series and species. SIBEC site index estimates and their standard errors are published online; however, a simplistic approach to calculating these standard errors was taken. New growth intercept models were developed from stem analysis data and were applied to SIBEC data collected in the Coastal Western Hemlock biogeoclimatic zone, very dry maritime subzone, 01 site series (CWHxm2/01) for Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. menziesii). A more appropriate approach to calculating the standard error of the mean site index estimate was derived and applied to the SIBEC data. The formula for the standard error requires knowledge of the covariances between growth intercept model predictions, which are unknown except when only one model is used to make the predictions. The results indicated that the corrected standard errors were substantially lower than the standard errors calculated using the current method. A typical SIBEC site index estimate is made up of data from growth intercept models, site index models, and stem analysis. Combining these data sources greatly complicates the standard error calculations, which makes their computation even more difficult than when only growth intercept models are used to estimate site index."-- Abstract.