Question

Discuss three reasons why a regression model can never fully capture the true relationships of the population.

Answer 1

When the relationship between independent and dependent variable are linear, regression provide a very good model. But not all the things in this world follow linear relationship. In this case it will be difficult to capture the true relationship of the population.
The regression model is easily affected by outliers in the data. If there are outliers in the data the coefficient of regression are inflated and which in turns affect the prediction made by the model. This is one of the reason why regression can never fully capture the true relationships of the population.
Regression easily gets overfitted such that the regression begins to model the random error (noise) in the data, rather than just the relationship between the variables. This most commonly arises when you have too many parameters compared to the number of samples.