Consider the following regression equation specied for 2-period panel data: where i = 1; 2; :::N and t = 1; 2. If you expect that β_1 is positive, but the correlation between Δx_i and Δu_i is...

Consider the following regression equation specied for 2-period panel data:

where i = 1; 2; :::N and t = 1; 2. If you expect thatβ_1 is positive, but the correlation between Δx_i and Δu_i is negative, then
what is the bias in the OLS estimator ofβ_1 in the first-differenced equation?