4.1.2. Outcome The AISP appears to have had a substantial effect on maize output, but some uncertainty surrounds the estimates due to other factors (e.g. the weather) influencing the data. Official estimates suggest that national maize harvests increased by around 1 million tonnes in 2005/6 rising to more than 2 million tonnes in the 2008/9 season (around 54% and 114%) compared to the 2002/3 and 2003/4 seasons. These estimates are, however,highly contentious. More conservative estimates by Dorward et al (2010) based on assumptions about average maize responses to fertilizer, put the increase in maize output at around 400,000 tonnes in 2005/6 to 1,000,000 tonnes in 2008/9 (corresponding to an increase of 23% and 54%) compared to pre-AISP harvests. These estimates by Dorward et al (2010) are derived by multiplying the estimated increase in fertilizer use with an estimated average fertilizer response rate, adjusting for weather, use of improved seeds and delivery delays. For the lack of better statistics, this approach seems reasonable, but the estimates must be viewed as highly uncertain. A few studies have tried to quantify the impact of the input subsidy based on a more stringent scientific (econometric) methodology. Ricker-Gilbert and Jayne (2010) try to estimate the dynamic effects of the AISP. They find that a fertilizer subsidy significantly increases maize production within the same year, and there are some indications of positive effects on maize production in subsequent seasons but these are surrounded by greater uncertainty. On the other hand, they find little evidence of a long-term effect on household assets or general wellbeing.
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