This will have an impact on the size of the aggregation bias: if the risk has a weak correlation across farms, the difference of the observed variability between the farm and the aggregated level is likely to be larger, leading to higher aggregation bias. In most countries, statistics show that the yield risk is much less correlated across farms, meaning that yield risk is more farm specific (Figure 1.7) . However, price risk is highly correlated across farms. If a farmer suffers from low prices, it is highly likely that other farmers experience similar adversity at the same time.