Upload
constance-little
View
52
Download
10
Embed Size (px)
DESCRIPTION
Chapter 2 Valuation, Risk, Return, and Uncertainty. Introduction. Introduction Safe Dollars and Risky Dollars Relationship Between Risk and Return The Concept of Return Some Statistical Facts of Life. Safe Dollars and Risky Dollars. A safe dollar is worth more than a risky dollar - PowerPoint PPT Presentation
Citation preview
1
Chapter 2 Valuation, Risk, Return, and
Uncertainty
2
Introduction Introduction Safe Dollars and Risky Dollars Relationship Between Risk and Return The Concept of Return Some Statistical Facts of Life
3
Safe Dollars and Risky Dollars A safe dollar is worth more than a risky
dollar• Investing in the stock market is exchanging
bird-in-the-hand safe dollars for a chance at a higher number of dollars in the future
4
Safe Dollars and Risky Dollars (cont’d)
Most investors are risk averse• People will take a risk only if they expect to be
adequately rewarded for taking it
People have different degrees of risk aversion• Some people are more willing to take a chance
than others
5
Choosing Among Risky Alternatives
Example
You have won the right to spin a lottery wheel one time. The wheel contains numbers 1 through 100, and a pointer selects one number when the wheel stops. The payoff alternatives are on the next slide.
Which alternative would you choose?
6
Choosing Among Risky Alternatives (cont’d)
$100$100$100$100
Average
payoff
–$89,000[100]$550[91–100]$0[51–100]$90[51–100]
$1,000[1–99]$50[1–90]$200[1–50]$110[1–50]
DCBA
Number on lottery wheel appears in brackets.
7
Choosing Among Risky Alternatives (cont’d)
Example (cont’d)Solution:
Most people would think Choice A is “safe.” Choice B has an opportunity cost of $90 relative
to Choice A. People who get utility from playing a game pick
Choice C. People who cannot tolerate the chance of any
loss would avoid Choice D.
8
Choosing Among Risky Alternatives (cont’d)
Example (cont’d)
Solution (cont’d): Choice A is like buying shares of a utility stock. Choice B is like purchasing a stock option. Choice C is like a convertible bond. Choice D is like writing out-of-the-money call
options.
9
Risk Versus Uncertainty Uncertainty involves a doubtful outcome
• What birthday gift you will receive• If a particular horse will win at the track
Risk involves the chance of loss• If a particular horse will win at the track if you
made a bet
10
Dispersion and Chance of Loss There are two material factors we use in
judging risk:• The average outcome
• The scattering of the other possibilities around the average
11
Dispersion and Chance of Loss (cont’d)
Investment A Investment B
Time
Investment value
12
Dispersion and Chance of Loss (cont’d)
Investments A and B have the same arithmetic mean
Investment B is riskier than Investment A
13
Concept of Utility Utility measures the satisfaction people get
out of something• Different individuals get different amounts of
utility from the same source– Casino gambling
– Pizza parties
– CDs
– Etc.
14
Diminishing Marginal Utility of Money
Rational people prefer more money to less• Money provides utility
• Diminishing marginal utility of money– The relationship between more money and added
utility is not linear
– “I hate to lose more than I like to win”
15
Diminishing Marginal Utility of Money (cont’d)
$
Utility
16
St. Petersburg Paradox Assume the following game:
• A coin is flipped until a head appears• The payoff is based on the number of tails
observed (n) before the first head• The payoff is calculated as $2n
What is the expected payoff?
17
St. Petersburg Paradox (cont’d)
Number of Tails Before First
Head Probability PayoffProbability
× Payoff
0 (1/2) = 1/2 $1 $0.50
1 (1/2)2 = 1/4 $2 $0.50
2 (1/2)3 = 1/8 $4 $0.50
3 (1/2)4 = 1/16 $8 $0.50
4 (1/2)5 = 1/32 $16 $0.50
n (1/2)n + 1 $2n $0.50
Total 1.00
18
St. Petersburg Paradox (cont’d)
In the limit, the expected payoff is infinite
How much would you be willing to play the game?• Most people would only pay a couple of dollars• The marginal utility for each additional $0.50
declines
19
The Concept of Return Measurable return Expected return Return on investment
20
Measurable Return Definition Holding period return Arithmetic mean return Geometric mean return Comparison of arithmetic and geometric
mean returns
21
Definition A general definition of return is the benefit
associated with an investment• In most cases, return is measurable• E.g., a $100 investment at 8%, compounded
continuously is worth $108.33 after one year– The return is $8.33, or 8.33%
22
Holding Period Return The calculation of a holding period return is
independent of the passage of time
• E.g., you buy a bond for $950, receive $80 in interest, and later sell the bond for $980
– The return is ($80 + $30)/$950 = 11.58%
– The 11.58% could have been earned over one year or one week
pricePurchase
GainCapitalIncomeReturn
23
Arithmetic Mean Return The arithmetic mean return is the
arithmetic average of several holding period returns measured over the same holding period:
iR
n
R
i
n
i
i
periodin return of rate the~
~mean Arithmetic
1
24
Arithmetic Mean Return (cont’d)
Arithmetic means are a useful proxy for expected returns
Arithmetic means are not especially useful for describing historical returns• It is unclear what the number means once it is
determined
25
Geometric Mean Return The geometric mean return is the nth root
of the product of n values:
1)~
1(mean Geometric/1
1
nn
iiR
26
Arithmetic and Geometric Mean Returns
Example
Assume the following sample of weekly stock returns:
Week Return Return Relative
1 0.0084 1.0084
2 -0.0045 0.9955
3 0.0021 1.0021
4 0.0000 1.000
27
Arithmetic and Geometric Mean Returns (cont’d)
Example (cont’d)
What is the arithmetic mean return?
Solution:
0015.04
0000.00021.00045.00084.0
~mean Arithmetic
1
n
i
i
n
R
28
Arithmetic and Geometric Mean Returns (cont’d)
Example (cont’d)
What is the geometric mean return?
Solution:
001489.0
10000.10021.19955.00084.1
1~
1(mean Geometric
4/1
/1
1
nn
iiR
29
Comparison of Arithmetic &Geometric Mean Returns
The geometric mean reduces the likelihood of nonsense answers• Assume a $100 investment falls by 50% in
period 1 and rises by 50% in period 2
• The investor has $75 at the end of period 2– Arithmetic mean = (-50% + 50%)/2 = 0%
– Geometric mean = (0.50 x 1.50)1/2 –1 = -13.40%
30
Comparison of Arithmetic &Geometric Mean Returns
The geometric mean must be used to determine the rate of return that equates a present value with a series of future values
The greater the dispersion in a series of numbers, the wider the gap between the arithmetic and geometric mean
31
Expected Return Expected return refers to the future
• In finance, what happened in the past is not as important as what happens in the future
• We can use past information to make estimates about the future
32
Definition Return on investment (ROI) is a term that
must be clearly defined• Return on assets (ROA)
• Return on equity (ROE)– ROE is a leveraged version of ROA
33
Standard Deviation and Variance
Standard deviation and variance are the most common measures of total risk
They measure the dispersion of a set of observations around the mean observation
34
Standard Deviation and Variance (cont’d)
General equation for variance:
If all outcomes are equally likely:
2
2
1
Variance prob( )n
i ii
x x x
2
2
1
1 n
ii
x xn
35
Standard Deviation and Variance (cont’d)
Equation for standard deviation:
2
2
1
Standard deviation prob( )n
i ii
x x x
36
Semi-Variance Semi-variance considers the dispersion only
on the adverse side• Ignores all observations greater than the mean• Calculates variance using only “bad” returns
that are less than average• Since risk means “chance of loss” positive
dispersion can distort the variance or standard deviation statistic as a measure of risk
37
Some Statistical Facts of Life Definitions Properties of random variables Linear regression R squared and standard errors
38
Definitions Constants Variables Populations Samples Sample statistics
39
Constants A constant is a value that does not change
• E.g., the number of sides of a cube• E.g., the sum of the interior angles of a triangle
A constant can be represented by a numeral or by a symbol
40
Variables A variable has no fixed value
• It is useful only when it is considered in the context of other possible values it might assume
In finance, variables are called random variables• Designated by a tilde
– E.g., x
41
Variables (cont’d) Discrete random variables are countable
• E.g., the number of trout you catch
Continuous random variables are measurable• E.g., the length of a trout
42
Variables (cont’d) Quantitative variables are measured by real
numbers• E.g., numerical measurement
Qualitative variables are categorical• E.g., hair color
43
Variables (cont’d) Independent variables are measured
directly• E.g., the height of a box
Dependent variables can only be measured once other independent variables are measured• E.g., the volume of a box (requires length,
width, and height)
44
Populations A population is the entire collection of a
particular set of random variables The nature of a population is described by
its distribution• The median of a distribution is the point where
half the observations lie on either side• The mode is the value in a distribution that
occurs most frequently
45
Populations (cont’d) A distribution can have skewness
• There is more dispersion on one side of the distribution
• Positive skewness means the mean is greater than the median
– Stock returns are positively skewed
• Negative skewness means the mean is less than the median
46
Populations (cont’d)Positive Skewness Negative Skewness
47
Populations (cont’d) A binomial distribution contains only two
random variables• E.g., the toss of a coin
A finite population is one in which each possible outcome is known• E.g., a card drawn from a deck of cards
48
Populations (cont’d) An infinite population is one where not all
observations can be counted• E.g., the microorganisms in a cubic mile of
ocean water
A univariate population has one variable of interest
49
Populations (cont’d) A bivariate population has two variables of
interest• E.g., weight and size
A multivariate population has more than two variables of interest• E.g., weight, size, and color
50
Samples A sample is any subset of a population
• E.g., a sample of past monthly stock returns of a particular stock
51
Sample Statistics Sample statistics are characteristics of
samples• A true population statistic is usually
unobservable and must be estimated with a sample statistic
– Expensive
– Statistically unnecessary
52
Properties of Random Variables
Example Central tendency Dispersion Logarithms Expectations Correlation and covariance
53
Example
Assume the following monthly stock returns for Stocks A and B:
Month Stock A Stock B
1 2% 3%
2 -1% 0%
3 4% 5%
4 1% 4%
54
Central Tendency Central tendency is what a random variable
looks like, on average The usual measure of central tendency is
the population’s expected value (the mean)• The average value of all elements of the
population
1
1( )
n
i ii
E R Rn
55
Example (cont’d)
The expected returns for Stocks A and B are:
1
1 1( ) (2% 1% 4% 1%) 1.50%
4
n
A ii
E R Rn
1
1 1( ) (3% 0% 5% 4%) 3.00%
4
n
B ii
E R Rn
56
Dispersion Investors are interest in the best and the
worst in addition to the average A common measure of dispersion is the
variance or standard deviation
22
22
i
i
E x x
E x x
57
Example (cont’d)
The variance ad standard deviation for Stock A are:
22
2 2 2 2
2
1(2% 1.5%) ( 1% 1.5%) (4% 1.5%) (1% 1.5%)
41
(0.0013) 0.0003254
0.000325 0.018 1.8%
iE x x
58
Example (cont’d)
The variance ad standard deviation for Stock B are:
22
2 2 2 2
2
1(3% 3.0%) (0% 3.0%) (5% 3.0%) (4% 3.0%)
41
(0.0014) 0.000354
0.00035 0.0187 1.87%
iE x x
59
Logarithms Logarithms reduce the impact of extreme
values• E.g., takeover rumors may cause huge price
swings• A logreturn is the logarithm of a return
Logarithms make other statistical tools more appropriate• E.g., linear regression
60
Logarithms (cont’d) Using logreturns on stock return
distributions:• Take the raw returns
• Convert the raw returns to return relatives
• Take the natural logarithm of the return relatives
61
Expectations The expected value of a constant is a
constant:
The expected value of a constant times a random variable is the constant times the expected value of the random variable:
( )E a a
( ) ( )E ax aE x
62
Expectations (cont’d) The expected value of a combination of
random variables is equal to the sum of the expected value of each element of the combination:
( ) ( ) ( )E x y E x E y
63
Correlations and Covariance Correlation is the degree of association
between two variables
Covariance is the product moment of two random variables about their means
Correlation and covariance are related and generally measure the same phenomenon
64
Correlations and Covariance (cont’d)
( , ) ( )( )ABCOV A B E A A B B
( , )AB
A B
COV A B
65
Example (cont’d)
The covariance and correlation for Stocks A and B are:
1(0.5% 0.0%) ( 2.5% 3.0%) (2.5% 2.0%) ( 0.5% 1.0%)
41
(0.001225)40.000306
AB
( , ) 0.0003060.909
(0.018)(0.0187)ABA B
COV A B
66
Correlations and Covariance Correlation ranges from –1.0 to +1.0.
• Two random variables that are perfectly positively correlated have a correlation coefficient of +1.0
• Two random variables that are perfectly negatively correlated have a correlation coefficient of –1.0
67
1
23456789101112131415
A B C D E F G H I J K
Year
AdamsFarm stock
return
MorganSausage
stockreturn
1990 30.73% 21.44% <-- =3%+0.6*B31991 55.21% 36.13%1992 15.82% 12.49%1993 33.54% 23.12%1994 14.93% 11.96%1995 35.84% 24.50%1996 48.39% 32.03%1997 37.71% 25.63%1998 67.85% 43.71%1999 44.85% 29.91%
Correlation 1.00 <-- =CORREL(B3:B12,C3:C12)
CORRELATION +1Adams Farm and Morgan Sausage Stocks
rMorgan Sausage,t = 3% + 0.6*rAdams Farm,t Annual Stock Returns, Adams Farm and Morgan Sausage
0%
5%
10%
15%
20%
25%
30%
35%
40%
45%
50%
10% 20% 30% 40% 50% 60% 70%Adams Farm
Mor
gan
Saus
age
68
181920212223242526272829303132333435363738394041
A B C D E F G H I
Stock A Stock BMonth Price Return Price Return
0 25.00 45.001 24.12 -3.58% 44.85 -0.33%2 23.37 -3.16% 46.88 4.43% <-- =LN(E23/E22)3 24.75 5.74% 45.25 -3.54%4 26.62 7.28% 50.87 11.71%5 26.50 -0.45% 53.25 4.57%6 28.00 5.51% 53.25 0.00%7 28.88 3.09% 62.75 16.42%8 29.75 2.97% 65.50 4.29%9 31.38 5.33% 66.87 2.07%
10 36.25 14.43% 78.50 16.03%11 37.13 2.40% 78.00 -0.64%12 36.88 -0.68% 68.23 -13.38%
Monthly mean 3.24% 3.47% <-- =AVERAGE(F22:F33)Monthly variance 0.23% 0.65% <-- =VARP(F22:F33)Monthly stand. dev. 4.78% 8.03% <-- =STDEVP(F22:F33)
Annual mean 38.88% 41.62% <-- =12*F35Annual variance 2.75% 7.75% <-- =12*F36Annual stand. dev. 16.57% 27.83% <-- =SQRT(F40)
CALCULATING THE RETURNS
69
444546474849505152535455565758596061626364
A B C D E F G H I JCOVARIANCE AND VARIANCE CALCULATION
Stock A Stock BReturn Return-mean Return Return-mean Product
-0.0358 -0.0682 -0.0033 -0.0380 0.00259 <-- =E48*B48-0.0316 -0.0640 0.0443 0.0096 -0.000610.0574 0.0250 -0.0354 -0.0701 -0.001750.0728 0.0404 0.1171 0.0824 0.00333
-0.0045 -0.0369 0.0457 0.0110 -0.000410.0551 0.0227 0.0000 -0.0347 -0.000790.0309 -0.0015 0.1642 0.1295 -0.000190.0297 -0.0027 0.0429 0.0082 -0.000020.0533 0.0209 0.0207 -0.0140 -0.000290.1443 0.1119 0.1603 0.1257 0.014060.0240 -0.0084 -0.0064 -0.0411 0.00035
-0.0068 -0.0392 -0.1338 -0.1685 0.00660
Covariance 0.00191 <-- =AVERAGE(G48:G59)0.00191 <-- =COVAR(A48:A59,D48:D59)
Correlation 0.49589 <-- =G62/(F37*C37)0.49589 <-- =CORREL(A48:A59,D48:D59)
=D48-$F$35
70
Linear Regression Linear regression is a mathematical
technique used to predict the value of one variable from a series of values of other variables• E.g., predict the return of an individual stock
using a stock market index Regression finds the equation of a line
through the points that gives the best possible fit
71
Linear Regression (cont’d)Example
Assume the following sample of weekly stock and stock index returns:
Week Stock Return Index Return
1 0.0084 0.0088
2 -0.0045 -0.0048
3 0.0021 0.0019
4 0.0000 0.0005
72
Linear Regression (cont’d)Example (cont’d)
-0.006
-0.004
-0.002
0
0.002
0.004
0.006
0.008
0.01
-0.01 -0.005 0 0.005 0.01
Return (Market)
Re
turn
(S
tock
)
Intercept = 0Slope = 0.96R squared = 0.99
73
R Squared and Standard Errors
Application R squared Standard Errors
74
Application R-squared and the standard error are used
to assess the accuracy of calculated statistics
75
R Squared R squared is a measure of how good a fit we get
with the regression line• If every data point lies exactly on the line, R squared is
100%
R squared is the square of the correlation coefficient between the security returns and the market returns• It measures the portion of a security’s variability that is
due to the market variability
76
1
23456789101112131415161718192021222324252627282930
A B C D E F G H I J K L
Date
S&P 500IndexSPX
MirageResorts
MIRJan-97 6.13% 16.18%Feb-97 0.59% 0.00%Mar-97 -4.26% -15.42%Apr-97 5.84% -5.29%
May-97 5.86% 18.63%Jun-97 4.35% 5.76%Jul-97 7.81% 5.94%
Aug-97 -5.75% 0.23%Sep-97 5.32% 12.35%Oct-97 -3.45% -17.01%Nov-97 4.46% -5.00%Dec-97 1.57% -4.21%Jan-98 1.02% 1.37%Feb-98 7.04% -0.54%Mar-98 4.99% 5.99%Apr-98 0.91% -9.25%
May-98 -1.88% -5.67%Jun-98 3.94% 2.40%Jul-98 -1.16% 0.88%
Aug-98 -14.58% -30.81%Sep-98 6.24% 12.61% Slope 1.469256 <-- =SLOPE(C3:C26,B3:B26)Oct-98 8.03% 1.12% 1.469256 <-- =COVAR(C3:C26,B3:B26)/VARP(B3:B26)Nov-98 5.91% -12.18%Dec-98 5.64% 0.42% Intercept -0.042365 <-- =INTERCEPT(C3:C26,B3:B26)
-0.042365 <-- =AVERAGE(C3:C26)-B28*AVERAGE(B3:B26)
R-squared 0.500072 <-- =RSQ(C3:C26,B3:B26)0.500072 <-- =CORREL(C3:C26,B3:B26)^2
SIMPLE REGRESSION EXAMPLE IN EXCEL
MIR Returns vs S&P500 ReturnsMonthly Returns, 1997-1998
y = 1.4693x - 0.0424
R2 = 0.5001-40%
-30%
-20%
-10%
0%
10%
20%
30%
-20% -15% -10% -5% 0% 5% 10%S&P500
MIR
77
Standard Errors The standard error is the standard deviation
divided by the square root of the number of observations:
Standard errorn
78
Standard Errors (cont’d) The standard error enables us to determine
the likelihood that the coefficient is statistically different from zero• About 68% of the elements of the distribution
lie within one standard error of the mean• About 95% lie within 1.96 standard errors• About 99% lie within 3.00 standard errors
79
Runs Test
A runs test allows the statistical testing of whether a series of price movements occurred by chance.
A run is defined as an uninterrupted sequence of the same observation. Ex: if the stock price increases 10 times in a row, then decreases 3 times, and then increases 4 times, we then say that we have three runs.
80
Notation
R = number of runs (3 in this example) n1 = number of observations in the first category.
For instance, here we have a total of 14 “ups”, so n1=14.
n2 = number of observations in the second category. For instance, here we have a total of 3 “downs”, so n2=3.
Note that n1 and n2 could be the number of “Heads” and “Tails” in the case of a coin toss.
81
Statistical Test
1 2
1 2
2 1 2 1 2 1 22
1 2 1 2
The z statistic computed is:
(thus z is a standard normal variable)
where
2 1
2 (2 )
( ) ( 1)
R xz
n nx
n n
n n n n n n
n n n n
82
Example
Let the number of runs R=23 Let the number of ups n1=20
Let the number of downs n2=30
Then the mean number of runs 25
The standard deviation 3.36
Yielding a z statistic of: 0.595
x
z
83
About 2.5% of the area under the normal curve is below a z score of -
1.96.
84
Interpretation
Since our z-score is not in the lower tail (nor is it in the upper tail), the runs we have witnessed are purely the product of chance.
If, on the other hand, we had obtained a z-score in the upper (2.5%) or lower (2.5%) tail, we would then be 95% certain that this specific occurrence of runs didn’t happen by chance. (Or that we just witnessed an extremely rare event)