OFRFA major US survey published in 2001, analyzed results from 150 growing seasons for various crops and concluded that organic yields were 95-100% of conventional yields - . Comparative yield studies are still scarce, and overall results remain "inconclusive". The issue of productivity is more complex than a summary of yield (production per land area), which was the measure used in these studies. Instead, productivity could be calculated in labour time rather than by land area. Organic methods often require more labor, providing rural jobs but increasing costs to urban consumers. Also, grain forms the majority of world agricultural production, and most of that is fed to animals, not humans—broad calculations of how much agriculture is feeding people is therefore complicated when feeding animals to feed people is factored in. The hidden costs of conventional agriculture are seldom addressed in productivity calculations. Conventional agriculture is based on importing energy, particularly in the form of fertilizer and other agrichemicals, machinery and fuel, and long-distance transport. The full cost of these inputs are not included. For example, maintenance of the airports and highways that allow easy transport are not factored into food costs. If airports were shut down, or highway systems compromised, however, there would be an immediate affect on the cost of food. More indirectly, it is argued that the cost of the side effects of chemical agriculture, like health care and environmental clean up, should be included in the cost of agribusiness. Instead, these hidden costs are paid by the public in other ways, such as through taxation to fund services like pollution control measures, and increased health care costs. Of course, many of these hidden cost factors are disputed, and they are difficult to investigate. Related to this is the amount of money that actually reaches the farmer. Currently, large-scale farms receive around 10-20% of the supermarket retail price. The other 80-90% is absorbed by the food distribution system for processing, transport, packaging and marketing. The organic argument holds that more efficient distribution, through decentralization of production (e.g. family farm vs. factory farm), and development of local and regional markets, would put more money in the hands of farmers, allowing for increased productivity.