A risk analyst at a bank is explaining to an intern the use of the Arbitrage Pricing Theory (APT) in estimating the expected return of a security. The risk analyst uses the following APT formula in the discussion:

$$R_i = E(R_i) + \beta_{i1}[I_1 - E(I_1)] + ... + \beta_{ik}[I_k - E(I_k)] + e_i$$

Which of the following is a correct interpretation of $\beta_{ik}$?