Empirical research on the profit impact of marketing strategy indicated that firms with a high market share were often quite profitable, but so were many firms with low market share. The least profitable firms were those with moderate market share. This was sometimes referred to as the hole in the middle problem. Porter's explanation of this is that firms with high market share were successful because they pursued a cost leadership strategy and firms with low market share were successful because they used market segmentation to focus on a small but profitable market niche. Firms in the middle were less profitable because they did not have a viable generic strategy.