Using 4 data point price 11 385 12 505 13 425 14 415 sqft 11 2254 12 2600 13 2800 14 3000 The std error of sqft on gretl is 0.112376 Using the formula s = sqrt[ ∑ ((e_i)^2/(n-2)) / (∑ (x_i - xbar)^2) ] x_i = the ith observation e_i = the ith error = y_i - yhat_i n = sample size xbar = mean of the x values gives 0.012628336