A researcher wants to include skill in a regression. Unfortunately, since there is no proper way to measure it, it is decided to leave it out. You read their work and realise you have access to data measuring skill. When you run the proper regression, you find that none of the original ? coefficients change. What would explain this?

a.

The covariance between skill and each of the other regressors is zero.

b.

The ? for skill is non-zero.

c.

The variance of skill is increasing.

d.

The covariance between skill and each of the other regressors is not zero.

A researcher wants to include skill in a regression. Unfortunately, sin