# Urbanization and Grain Production Pattern of China: Dynamic Effect and Mediating Mechanism
## 3 Materials and Methods
### Variable Selection and Data Sources  
#### 3.2.1 Variable Selection  
1. Explained variable: grain production pattern (GPP). The macro-scale changes in the GPP are usually characterized by the grain production concentration index (GPCI), which represents the contribution of a region's grain production to the national total--i.e., the percentage of a region's grain production in the national total. The calculated concentration index also reflects the changing standing of a region's grain production in the country through time-series changes [11; 14]. 2. Core explanatory variable: urbanization (URBAN). Urbanization is a comprehensive system that includes multidimensional features such as population size, land expansion, spatial carrying capacity, economic growth, and living standards. By referring to existing studies, relevant indicators were selected from five dimensions, including population, land, space, economy, and livelihood [47]. Specifically, population urbanization was characterized by the urbanization rate of the resident population. Land urbanization was characterized by the area of built-up urban regions. Spatial urbanization was characterized by urban population density. Economic urbanization was characterized by the proportion of non-agricultural industries in the GDP. Social urbanization was characterized by urban road area per capita. In this paper, the indicators are assigned weights and evaluated comprehensively for urbanization by the entropy method. 3. Mediator variables 1. Cropland utilization. Characterized by the multiple crop index (MCI), cropland utilization was calculated as the ratio of grain crop planting area to the total cropland area [26]. 2. Planting structure (PS). As the indicator of agricultural production restructuring, the PS was represented as the ratio of grain crop planting area to the total crop planting area [48]. 3. Agricultural technology progress (ATECH). Mechanization services effectively substitute the labor factor and reflect technological progress and intensive cropland utilization [49]. In this paper, the comprehensive mechanization rate of tillage, sowing, and harvesting of grain crops was used as a substitution variable for ATECH. Comprehensive mechanization rate = mechanized tillage rate \(\times\) 40% + mechanized sowing rate \(\times\) 30% + mechanized harvesting rate \(\times\) 30%. Here, the mechanized tillage rate is the ratio of mechanized tillage area to total cropland area. The mechanized sowing rate is the ratio of mechanized sowing area to total sowing area. The mechanized harvesting rate is the ratio of mechanized harvesting area to total sowing area. The comprehensive mechanization rate is expressed in the form of a percentage. 4. Control variables A range of socioeconomic and natural condition factors affecting the GPP were set as control variables in the model. Specifically, the economic growth (GDP) was expressed as the natural logarithm of GDP per capita. The upgrading of the industrial structure (STRUC) was expressed as the ratio of the value added of the tertiary industry to the value added of the secondary industry. The urban-rural income gap (GAP) was expressed as the ratio of the per capita disposable income of urban residents to the per capita net income of rural residents. The educational level of the population (EDU) was calculated as a weighted summary of the number of years of education at each level and its proportion of the total population: specifically, 0 years for illiteracy, 6 years for elementary school, 9 years for junior high school, 12 years for high school and technical secondary school, 15 years for junior college, 16 years for undergraduate, and 19 years for postgraduate. The openness of economy (OPEN) was represented as the ratio of total import and export trade volume in GDP. The fiscal support to agriculture (FISCAL) was represented as the proportion of expenditure on agriculture, forestry, and water affairs in the general budget expenditure of local finance.