4 Advanced Modelling in Finance
and automated in a VBA macro. By using the array functions in Excel and VBA, we detail
how the points on the efficient frontier can be generated. The development of portfolio
theory is divided into three generic problems, which recur in subsequent chapters.
Chapter 7 looks at (equity) asset pricing, starting with the single-index model and
the capital asset pricing model (CAPM) and concluding with Value-at-Risk (VaR). This
introduces the assumption that asset log returns follow a normal distribution, another
recurrent theme.
Chapter 8 covers performance measurement, again ranging from single-parameter
measures used in the very earliest days to multi-index models (such as style analysis) that
represent current best practice. We show, for the first time in a textbook, how confidence
intervals can be determined for the asset weights from style analysis.
Chapter 9 introduces the second application part, that dealing with options on equities.
Building on the normal distribution assumed for equity log returns, we detail the creation
of the hedge portfolio that is the key insight behind the Black–Scholes option valuation
formula. The subsequent interpretation of the option value as the discounted expected
value of the option payoff in a risk-neutral world is also introduced.
Chapter 10 looks at binomial trees, which can be viewed as a discrete approxima-
tion to the continuous normal distribution assumed for log equity prices. In practice,
binomial trees form the backbone of numerical methods for option valuation since they
can cope with early exercise and hence the valuation of American options. We illustrate
three different parameter choices for binomial trees, including the little-known Leisen and
Reimer tree that has vastly superior convergence and accuracy properties compared to the
standard parameter choices. We use a nine-step tree in our spreadsheet examples, but the
user-defined functions can cope with any number of steps.
Chapter 11 returns to the Black–Scholes formula and shows both its adaptability
(allowing options on assets such as currencies and commodities to be valued) and its
dependence on the asset price assumptions.
Chapter 12 covers two alternative ways of calculating the statistical expectation that
lies behind the Black–Scholes formula for European options. These are Monte Carlo
simulation and numerical integration. Although these perform less well for the simple
options we consider, each of these methods has a valuable role in the valuation of more
complicated options.
Chapter 13 moves away from the assumption of strict normality of asset log returns and
shows how such deviation (typically through differing skewness and kurtosis parameters)
leads to the so-called volatility smile seen in the market prices of options. Efficient
methods for finding the implied volatility inherent in European option prices are described.
Chapter 14 introduces the third application part, that dealing with options on bonds.
While bond prices have characteristics that are different from equity prices, there is a
lot of commonality in the mathematical problems and numerical methods used to value
options. We define the term structure based on a series of zero-coupon bond prices, and
show how the short-term interest rate can be modelled in a binomial tree as a means of
valuing zero-coupon bond cash flows.
Chapter 15 covers two models for interest rates, those of Vasicek and Cox, and Ingersoll
and Ross. We detail analytic solutions for zero-coupon bond prices and options on zero-
coupon bonds together with an iterative approach to the valuation of options on coupon
bonds.
Chapter 16 shows how the short rate can be modelled in a binomial tree in order
to match a given term structure of zero-coupon bond prices. We build the popular