To summarize, as diversification increases, the total variance of a portfolio approaches the systematic variance, defined as the variance of the market index multiplied by the square of the portfolio sensitivity coefficient, β2P. This is shown in Figure 8.2.Figure 8.2 shows that as more and more securities are combined into a portfolio, the portfolio variance decreases because of the diversification of firm-specific risk. However, the power of diversification is limited. Even for very large n, part of the risk remains because of the exposure of virtually all assets to the common, or market, factor. Therefore, systematic risk is said to be nondiversifiable.This analysis is borne out by empirical evidence. We saw the effect of portfolio diversi- fication on portfolio standard deviations in Figure 7.2. These empirical results are similar to the theoretical graph presented here in Figure 8.2.