Critics therefore argue that farmers do not get any of the higher price under Fairtrade. Nor is there any evidence that they get higher prices as a result of better marketing: the cooperatives sometimes pay farmers a higher price than farmers do, sometimes less, but there is no evidence on which is more common. Farmers do, however, incur extra costs in producing Fairtrade, so they certainly do lose money from Fairtrade membership in some cases. There is little or no research on the extra costs incurred, or the effect of Fairtrade membership on the income of farmers. However, research by Overseas Development Institute found that a "wide variety of qualitative studies have found positive effects of Fairtrade certification on the incomes of producers".