Table 10.1 contains the variable definitions and means of the independent and trait variables. Independent variables are defined only in the case of the first data set. We have the definitions as well as means of trait variables for both data sets, and can characterize the independent variables contained in the first data set. They indicate that 86% of observations belonged to kharif season and 88% of them were under irrigated conditions. The average length of varietal use after their release was 7.2 years. In the districts in question, 45% of the farmers were literate. In these districts, the road length index increased from 1 in 1955-1959 to 2.29 in the period 1977-1989, and they had 44% of the cropped area under irrigation. The variable means of extension workers per farm, index of rice area and index of rice yield are reported in logarithmic form. For these districts, the average research stock variable was computed to be 4.76.
The means of the trait variables presented for both the data sets are more relevant for the present study. They indicate the degree of disease and pest resistance embedded into the varieties in use in the 45 districts of the first data set and the five states of the second data set. In the first data set, the rice varieties under use have the following disease and pest resistance traits. On average, 11% of them are resistant to blast, 10% to bacterial leaf blight, 3% to bacterial leaf stripe, 24% to rice tungro virus and 1% to sheath blight. Similarly, 13% of them are resistant to brown plant hopper, 7% to gall midge and 8% to stem borers. The second data set reports a different set of trait values for disease and pest resistance in the states under consideration. The varieties in vogue in the sample contain, on average, the following degrees of disease and pest resistance: 19% to rice blast; 12% to bacterial leaf blight; 13% to rice tungro virus; and 2% to sheath blight. They also contain resistance to the insect pests to the extent of 12% to brown plant hopper, 11% to green leaf hopper, 4% to white-backed plant hopper, 16% to gall midge, and 6% to stem borer.
Table 10.1. Variable definitions (means), Indian district and state variety data sets.
Dependent: ln(varlety yield) — ln(district average yield, all varieties)
KARIF: dummy = 1 if kharif trial 0.86
IRRI: dummy = 1 if irrigated trial 0.88
VARAGE: years since release of variety 7.2
LEXF: ln(extension staff per farm) 2.46
LITERACY: per cent literate 0.45 NINCA: net irrigated area (not cropped area) IROADS: index of road length = 1 in 1955-1959 LIARICE: index of rice area = 1 in 1955-1959
LVIARICE: index of rice yield = 1 in 1955-1959 0.66
RAINFALL: annual rainfall 4.00
RESEARCH: research stock (Evenson et al., 1996) 4.76
BL: dummy variable = 1 if resistant to blast 0.11
BLB: dummy variable = 1 if resistant to bacterial leaf blight 0.10
BLS: dummy variable = 1 if resistant to bacterial leaf stripe 0.03
RTV: dummy variable = 1 if resistant to rice tungro virus 0.24
SHBL: dummy variable = 1 if resistant to sheath blight 0.01
BPH: dummy variable = 1 if resistant to brown plant hopper 0.13
GLH: dummy variable = 1 if resistant to green leaf hopper 0.07 WBPH: dummy variable = 1 if resistant to white-backed plant hopper 0.02
GM: dummy variable = 1 if resistant to gall midge 0.17
SB: dummy variable = 1 if resistant to stem borers 0.08
An attempt is made to estimate the contribution of the above trait values to rice yield by regressing the yield by variety on the trait values of different varieties. For the district data set, a number of district variables are specified as control variables. In addition, dummy variables for agroclimatic zones are included in the district regressions. For the state data set, state X year dummy variables are included for all state X year combinations. This effectively means that variety yields are compared with the state-year mean yields.
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