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the sample, no difference was found, except a linear increasing trend for coffee production in Vietnam. Bt cotton introduction was found to have increased trend cotton production, and the effect was robust across various specifications. Indeed, after controlling for Bt cotton introduction, a decreasing linear trend was observed in cotton production in China. None of the three support variables defined were found to have a robust effect on the sample crop production. For instance, the NRA increased the sample crop production at the aggregate level, but the effect disappeared when the effects were disaggregated at the individual crop level. In the latter case, an increase in the short-run own-price elasticity of the cashew supply was observed. When the NRA estimates received for each commodity—relative to the NRA for all agricultural products covered in Anderson and Valenzuela (2008) for the same country, defined as the RRA—were included, only in the case of tobacco was the RRA found to increase production. In other cases, no effect was found. For tobacco, the short-run ownprice elasticity estimate became statistically insignificant when the RRA was included. The effects of agricultural policy reforms on the sample supply were discernible only when the sample was limited to those countries considered unsupportive of the commodity in question. Then, the short-run own-price elasticity of supply decreased after reforms.
Annex Robustness Tests Preliminary to the panel analysis, equation (3.4) was individually estimated for each country/commodity combination in the sample. Due to the limited number of observations, the individual regressions were run over the post-1980 period, except for cashew in Mozambique, coffee in Uganda and Vietnam, and cotton in Zambia. In these instances, the series begin in 1990. Estimates are presented in table 3A.2. Production and producer price series are nonstationary for all sample pairs, except that nonstationarity can be rejected at 10 percent for coffee in Uganda. Augmented Dickey-Fuller (ADF) test results are given in table 3A.3. Therefore, in order to address nonstationarity, equation (3.4) was estimated in differences for the individual country/commodity combinations. Table 3A.4 shows the regression results.8