Omitted covariates is a term generally found in the connection with regression modelling, where the model has been incompletely specified by not including significant covariates. The omission might be due either to an incorrect conceptual understanding of phenomena under study or to an inability to collect the data on all the relevant factors related to the outcome under study. Mis-specifying regression models in this manner can result in seriously biased estimates of effects of the covariates actually included in model.