The multiproduct (3-goods) specification is the author's preferred model: the hypothesis that it is superior to the single-output model is 'clearly accepted', and the multiproduct models give 'more efficient estimates'. The 3-goods unrestricted model is the fully general one used for the output/demand elasticities (Table 8). || 'our hypothesis that the multiproduct specification is superior to the single output model is clearly accepted' (p.121); 'our conclusion is that the multiproduct models give more efficient estimates' (p.119)
Larsson, J. (2006): "Four Essays on Technology, Productivity and Environment." Ph.D. Thesis, Gothenburg University: School of Business, Economics and Law, Sweden