Table 4 Description of explanatory variables

NM

Number of net migrants

If i = 1(x), expected urban wage$1\left(x\right)\ast \sum$ urban hukou _j

Ewu-gap

−expected urban wage _2(x)∗urban hukou _1(x)

If i = 2(x), expected urban wage _2(x)∗urban hukou _1(x)

−expected urban wage _1(x)∗urban hukou _2(x)

If i = 3(x), -expected urban wage _1(x)∗urban hukou _j(x);

j = 1…18, i ≠j,1(x) stands for the highest expected urban wage city

If i = 1(x), city population$1\left(x\right)\ast \sum$ agricultural hukou _j

P-gap

−city population _2(x)∗agricultural hukou _1(x)

If i = 2(x), city population _2(x)∗agricultural hukou _1(x)

−city population _1(x)∗agricultural hukou _2(x)

If i = 3(x), -city population _1(x)∗agricultural hukou _j(x)

j = 1…18, i ≠j,1(x) stands for the biggest city population city

If i = 1(x), capital stock$1\left(x\right)\ast \sum _j$ agricultural hukou

−capital stock _2(x)∗agricultural hukou _1(x)

K-gap

If i = 2(x), capital stock _2(x)∗agricultural hukou _1(x)

−capital stock _1(x)∗agricultural hukou _2(x)

If i = 3(x), -capital stock _1(x)∗agricultural hukou _j(x)

j = 1…18, i ≠j,1(x) stands for the largest amount of capital stock city

If i = 1(x), single female$1\left(x\right)\ast \sum$single female _j

−single female _2(x)∗single female _1(x)

SFP-gap

If i = 2(x), single female _2(x)∗single female _1(x)

−capital stock _1(x)∗single female _2(x)

If i = 3(x), -single female _1(x)∗single female _j(x)

j = 1…18, i ≠j,1(x) stands for the smallest number of single female city

If i = 1(x), urban hukou$1\left(x\right)\ast \sum$ agricultural hukou _j

−urban hukou _2(x)∗agricultural hukou _1(x)

UH-gap

If i = 2(x), urban hukou _2(x)∗agricultural hukou _1(x)

−urban hukou _1(x)∗agricultural hukou _2(x)

If i = 3(x), -urban hukou _1(x)∗agricultural hukou _j(x)

j = 1…18, i ≠j,1(x) stands for the biggest number of urban hukou city