unequal sample size and linear regression

Question

Can i use simple linear regression when there is unequal sample sizes for the dependent and independent variable? Will this be a problem?

That is; y=a+bx+epsilon, where y and x have unequal sample sizes.

Answer 1

If you have a data point that lacks either a value for the dependent or the independent variable, the data point does not carry any meaningful information and hence it is pretty much useless.

For example, assume you are investigating the influence of education on income and in your sample you have a person who earns $100,000 per year, but you don’t know his education level. Such information does not tell you anything about the relation between education and income, simply because you have no idea what his education level is.

Therefore you can only meaningfully use observations for which both the dependent and independent values are known.