66 



Agricultural Research and Productivity 



where 



K. (68) Stock of country fs knowledge in 1968: sum of 

 counts of articles in Plant Breeding Abstracts from 

 1948 10 1968 



Average rate of yield increases over the period 

 1948-68 



Average rate of change of yield for the period 

 1920-39 (set at zero for countries for which earlier 

 yields were not available). 



% 



Table 4.1: Rate Regressions (Equation 4.11) 



Notes: 

 No. of observations: Wheat 64, Maize 49. 

 Deflator: Area deflator (d^). 

 in parentheses: ^statistics. 



Estimation: The estimates were prepared in two stages. First, the average rates 

 of increases for wheat and for maize (allowing for area effects) were calculated 

 for each country from the equation 



(a) v.(t) 



aA (t)eP' u(t) 



where 



y(t) yield in country in year / 



A (t) area harvested 



u (i) disturbance. 



The estimated P values for the period 1948-68 are reported in appendix 4. A 

 columns 2, 7. 



in the second stage, equation 4.1 1 of the text was estimated. 



Regression estimates of equation 4.11 were weighted by the average square 

 deviation from the regressions of equation a for wheat and maize, respectively. 



