Abstract: Methods, systems, apparatus and articles of manufacture to generate projection factors are disclosed. An apparatus to reduce panel imbalance errors includes a data analyzer to identify a retailer in a geographic region indicative of shopping bias. The data analyzer also is to identify households of interest in the geographic region having combined panel data, the combined panel data representing core panelist data and auxiliary data. The apparatus also includes a modeling engine to calculate potential spending of each household at one or more stores of the retailer. The potential spending is based on observed spending. The apparatus also includes a projection engine to reduce panel imbalance errors by calculating projection weights for the combined panel based on (a) the potential spending at the one or more stores and (b) social or demographic representation data of the combined panel.