Ordinary least squares estimation is subject to heterogeneity bias if . 答案选项组 the regression model exhibits heteroskedasticty the unobserved effect is correlated with the observed explanatory variables the regression model includes a lagged dependent variable the explanatory variables do not change over time

Unobserved effect.

Step-by-step explanation:

The unobserved effect of heterogeneity is correlated with the observed explanatory variables. Population heterogeneity is bias in unobserved pre treatment factors which affect the outcome even without treatment.

D

Step-by-step explanation:

problem → f(x) = 3x + 1, g(x) = x2 - 6, find (f - g)(x).

f(x)=3x+1,g(x)=x2-6,(f-g)(x)=?

f(x)=3x+1

g(x)=x2-6

Now (f-g)(x)

 =f(x)-g(x)

=(3x+1)-(x2-6)

=3x+1-x2+6

=3x+7-x2

=-x^2 + 3x + 7