In an important study reviewing the literature on econometric studies of the relationship between advertising and sales Clarke (Clarke, Darral G. 1976. Econometric measurement of the duration of advertising effects on sales. J. Marketing Res. 13 (November) 345--357.) concluded that the implied...

Conditions are determined under which (a) the sum of forecasts of sales in market segments is preferred to a forecast of the whole market and (b) a forecast of an individual market segment is preferred to a forecast obtained through proration of a forecast of the whole market. The comparisons in...