Cảm ơn CAMTIEU nhiều nhé, nhưng mình muốn hỏi thêm đoạn này. Minh đọc sách ứng dụng trong kinh tế có đoạn :
Data in which the variances of the error terms are not equal, in
which the error terms may reasonably be expected to be larger for some points or ranges of the data than for others, are said to suffer from heteroskedasticity. The standard warning is that in the presence of heteroskedasticity, the regression coefficients for an ordinary least squares regression are still unbiased, but the standard errors and confidence intervals estimated by conventional procedures will be too narrow, giving a false sense of precision

Nhưng không biết dịch heteroskedasticity là chi hết bí quá rồi !