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8/28/14 Dynamic Equity Models 1 Dynamic Equity Models Learning Objec>ves Simula>on Daily, monthly, annual sta>s>cal rela>onships Lognormal probability density Stochas>c differen>al equa>on Con>nuous >me price process Exact solu>on Price and return probabili>es in con>nuous >me Probability basics for op>on deriva>ves 2 More Simula>on 3 Perform a stock price simula>on for which current stock price, S 0 = $40.00, the expected monthly con>nuously compounded mean rate of return, u, is 1%, and the expected standard devia>on, s, is 5%. Perform the simula>on with daily >me increments for one year. Use floa>ng point >me, annualized, μ and σ, sta>s>cs. Run the simula>on 10,000 >mes. years 000 . 1 T years 004 . 252 1 t % 321 . 17 12 s % 000 . 12 12 u = = = Δ = = σ = = μ 004 . 17321 . z 004 . 12 . t 004 . t t σ z t μ t t t e S S e S S + + Δ + Δ Δ + = = Simula>on: 4 $0 $5 $10 $15 $20 $25 $30 $35 $40 $45 $50 $55 $60 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00 Stock Price Time [years] 004 . 17321 . z 004 . 12 . t 004 . t t σ z t μ t t t e S S e S S + + Δ + Δ Δ + = =

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Page 1: Dynamic equity price pdf

8/28/14  

Dynamic  Equity  Models   1  

Dynamic  Equity  Models    

Learning  Objec>ves    

¨  Simula>on    ¤  Daily,  monthly,  annual  sta>s>cal  rela>onships  

¨  Lognormal  probability  density  ¨  Stochas>c  differen>al  equa>on  ¨  Con>nuous  >me  price  process  ¨  Exact  solu>on    ¨  Price  and  return  probabili>es  in  con>nuous  >me    ¨  Probability  basics  for  op>on  deriva>ves    

2  

More  Simula>on  3  

Perform    a  stock  price  simula>on  for  which  current  stock  price,  S0  =  $40.00,  the  expected  monthly  con>nuously  compounded  mean  rate  of  return,  u,  is  1%,  and  the  expected  standard  devia>on,  s,  is  5%.    Perform  the  simula>on  with  daily  >me  increments  for  one  year.      Use  floa>ng  point  >me,  annualized,  µ  and  σ,  sta>s>cs.      Run  the  simula>on  10,000  >mes.  

years      000.1T

years      004.2521t

%321.1712s

%000.1212u

=

==Δ

=⋅=σ

=⋅=µ

004.17321.z    004.12.t004.t

tσz    tμttt

eS      S

eS      S

⋅⋅+⋅⋅+

Δ⋅⋅+Δ⋅⋅Δ+

=

=

Simula>on:  4  

$0

$5

$10

$15

$20

$25

$30

$35

$40

$45

$50

$55

$60

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00

Stock  Price    

Time  [years]

004.17321.z    004.12.t004.t

tσz    tμttt

eS      S

eS      S⋅⋅+⋅

⋅+

Δ⋅⋅+Δ⋅⋅Δ+

=

=

Page 2: Dynamic equity price pdf

8/28/14  

Dynamic  Equity  Models   2  

Simula>on:  5  

-­‐6% -­‐5% -­‐4% -­‐3% -­‐2% -­‐1% 0% 1% 2% 3% 4% 5% 6%Natural  Log  Daily  Return  Rate

From  Simulation DailyMean  rate:  u 0.04859%Standard  deviation:  s   1.09460%

Simula>on:  6  

$20 $25 $30 $35 $40 $45 $50 $55 $60 $65 $70 $75 $80 $85 $90 $95Stock  Price  At  1  Year

M[ST] 45.09$      E[ST] 45.91$      Min[ST] 23.95$      Max[ST] 93.91$      

From  input    

$45.78                  e$40.00                  

eS]E[S

$45.10                    e$40.00                    

eS]M[S

1.0.135

Tμ0T

1.0.12

Tμ0T

*

=

⋅=

⋅=

=

⋅=

⋅=

The  median  price  is  the  5,000th  in  an  ordered  list  of  10,000  simulated  prices  at  T=1.0  years.    The  expected  price  is  the  average  of  the  10,000  prices.    

From  simula>on  

Lognormal  PDF  7

The  lognormal  pdf  is  •  Asymmetric  

•  Mode,  median,  and  mean  not  equal  

•  Never  nega>ve  •  Over  >me  the  mode,  

median,  and  mean  driZ  further  apart  

•  Over  >me  the  distribu>on  skews  more  posi>vely    

In  the  standard  price  theory  Simple  rates,  future  value  factors,  and  asset  prices  are  distributed  lognormal        

Return  Rate  and  Future  Value  Factor  PDFs    8  

[ ][ ]    uvEvM

==

( )2su,N~  v

( )        s  ,N~ 2µ

[ ][ ]µ=

µ

EM

( )        e~e2u,sNv

[ ][ ] *uv

uv

eeE              

   eeM

=

=

( )2,Nv12 e~e σµ⋅

[ ] [ ] *

eeE                eeM v12v12 µ⋅µ⋅ ==

Page 3: Dynamic equity price pdf

8/28/14  

Dynamic  Equity  Models   3  

[ ]tt,μN~SS

ln

tσztμSS

ln

tσztμ)ln(S)ln(S

wdσtμ)ln(S)ln(S

   dwσdt    dln(S)

2

0

t

0

t

t0t

0t

⋅σ⋅⎟⎟⎠

⎞⎜⎜⎝

⋅⋅+⋅=⎟⎟⎠

⎞⎜⎜⎝

⋅⋅+⋅+=

⋅+⋅+=

⋅+⋅µ=

Exact  Solu>on  9  

The  differen>al  equa>on  for  dln(S)  is    

The  solu>on  with  ini>al  condi>on  is      

At  >me  t  the  natural  log  of  price  ln(St)  is  distributed  normally  as              Therefore  

[ ]

[ ]

[ ]

[ ][ ] t

t

tt

tσ  t,μN0t

tσ  t,μ)ln(SNt

0t

*

*

*0

eSE

eSM

eS~S

e~S

tσ  t,μ)ln(SN~)ln(S

⋅µ

⋅µ

⋅⋅

⋅⋅+

=

=

⋅⋅+

Simula>on  10  

( )

[ ]

[ ][ ]

[ ] [ ] [ ]( ) f    for  Variance          fEfEfVar

f  for  Median                                                        eM[f]

f          for  moment  2                                        e  fE

f  for  moment  1                                                  efE

f  for  moment  k                                    efE

e~er1f

22

u

nds2u22

st2su

th2skukk

)N(u,sv

2

2

22

2

−=

=

=

=

=

=+≡

⋅+⋅

+

⋅+⋅

1ea

)a1ln(u2suu

*u

*

2*

−=

+=

+=

1eg

)g1ln(uu −=

+=

[ ] [ ] [ ] [ ]( )  fEfEfVarrVard 222 −===

Specified  Rate  of  return:  u 1.0%Standard  deviation,  s 5.0%Annual  frequency,  m   12                    

Computed  

Variance,  s2 0.00250  Expected  rate  of  return,  u* 1.12500%Expected  first  moment  of  f 1.01131  Expected  second  moment  of  f 1.02532  Simple  mean  rate,  a   1.13135%Geometric  rate,  g   1.00502%Simple  standard  deviation,  d 5.05973%

Monthly    Statistics  

Simula>on  11  

[ ]

[ ][ ][ ] [ ] [ ]( )22

222

2

2kkk

fEfEfVar

     e  fE

efE

efE

2

2

22

−=

=

=

=

σ⋅+µ⋅

σ+µ

σ⋅+µ⋅

1e

)1ln(2

*

*

2*

−=α

α+=µ

σ+µ=µ

µ

1e

)1ln(

−=γ

γ+=µµ

[ ] [ ] [ ] [ ]( )  fEfEfVarVar 222 −==α=δ

Specified  Rate  of  return:  u 1.0%  µ 12.00000%Standard  deviation,  s 5.0% σ 17.32051%Annual  frequency,  m   12                    

Computed  

Variance,  s2 0.00250   σ2 0.03000      Expected  rate  of  return,  u* 1.12500%  µ* 13.50000%Expected  first  moment  of  f 1.01131   1.14454      Expected  second  moment  of  f 1.02532   1.34986      Simple  mean  rate,  a   1.13135% α 14.45368%Geometric  rate,  g   1.00502% γ 12.74969%Simple  standard  deviation,  d 5.05973% δ 19.97357%

Monthly    Statistics   Annual  Statistics  

Computed  

Computed  

Simula>on  12  

Specified   Computed  Rate  of  return:  u 1.0%  µ 12.00000%  µ Δt 0.04762%Standard  deviation,  s 5.0% σ 17.32051% σ √Δt 1.09109%Annual  frequency,  m   12                     m 252

Computed   Computed  

Variance,  s2 0.00250   σ2 0.03000       σ2 t 0.00012  Expected  rate  of  return,  u* 1.12500%  µ* 13.50000%  µ

∗ Δt 0.05357%Expected  first  moment  of  f 1.01131   1.14454       1.00054  Expected  second  moment  of  f 1.02532   1.34986       1.00119  Simple  mean  rate,  a   1.13135% α 14.45368% 0.05359%Geometric  rate,  g   1.00502% γ 12.74969% 0.04763%Simple  standard  deviation,  d 5.05973% δ 19.97357% 1.09171%

Monthly    Statistics   Annual  Statistics  

Daily  Statistics  

Computed  

Computed  

Page 4: Dynamic equity price pdf

8/28/14  

Dynamic  Equity  Models   4  

Daily  Sta>s>cs    13  

( )

( ).04763%g          

10.45$g140$]M[S

.04762%u          10.45$e40eS]M[S

%05356.u          

78.45$e40$eS]E[S

%.05357a            45.78$a140$]E[S

252T

252umu0T

*

252umu0T

mT

**

=

=+⋅=

=

=⋅=⋅=

=

=⋅=⋅=

=

=+⋅=

⋅⋅

⋅⋅

Price  as  a  Stochas>c  Diff  Eqn    14  

ΔwσΔtμSΔS * ⋅+⋅= ΔtzΔw

SSS ttt

⋅=

−=Δ Δ+

dwσSdtμSdS * ⋅⋅+⋅⋅= dtzdw ⋅=

Difference  eqn  for  price  as  geometric  Brownian  mo>on  with  posi>ve  expected  rate  of  return      

Transform  to  a  differen>al  eqn  as  Δt  -­‐>  dt  with  the  goal  to  solve  the  eqn  for  price,  S      

( )SfF =

To  understand  stochas>c  differen>al,  dS,  introduce  F  which  is  a  func>on  of  stochas>c  process,  S.    S  is  dependent  on  Weiner  process,  w.      

µ:  con>nuously  compounded  natural  log  mean  rate  of  return      µ*:  con>nuously  compounded  simple  mean  or  expected  rate  of  return      

Stochas>c  Differen>al,  dF    15  

terms  order  higher  dSSF

21dS

SFdt

tFdF 2

2

2

+∂

∂⋅+

∂+

∂=

2*2

2* dw)SσdtS(μ

SF

21        dw)SσdtS(μ

SF        dt

tF        dF ⋅⋅+⋅⋅

∂⋅+⋅⋅+⋅⋅

∂+

∂=

dwSσSFdtSσ

SF

21

tFSμ

SFdF 22

2

2* ⋅⋅

∂+⋅⎟⎟

⎞⎜⎜⎝

⎛⋅⋅

∂⋅+

∂+⋅⋅

∂=

Ignore  dt2  and  dw·∙dt  terms  and  subs>tute    dw2  =  dt  which  will  be  explained  on  the  next  slide.      

Write  dF  as  a  Taylor  series  expansion      

Subs>tute  dS  into  dF    

Stochas>c  Differen>al,  dF    16  

[ ] [ ] [ ] 0zEdtdtzEdwE =⋅=⋅= [ ] [ ] [ ] dtzEdt)dtz(EdwE 222 =⋅=⋅=

[ ] [ ]( )[ ]

[ ] dt1dtzEdt                                  

0dtzE                                  

dwEdwE)dw(VAR

2

2

22

=⋅=⋅=

−⋅=

−= ( )[ ] [ ]( )[ ] ( )

[ ]0dt3dt                                      

                             dtzEdt                                      

dtdtzE                                      

dwEdwE)(dw  VAR

22

242

224

22222

=−⋅=

−⋅=

−⋅=

−=

dw  ∼  N(0,dt)                                                                                                    dw2  ∼  N(dt,0)        Stochas>c                                Determinis>c      

Determine:    E[dW],    E[dW2],    VAR[dW],    VAR[dW2]  to  resolve  dw2  =  dt    

Page 5: Dynamic equity price pdf

8/28/14  

Dynamic  Equity  Models   5  

Probability  Distribu>ons  Related  to  dw  and  dw2    17  

-­‐4 -­‐3 -­‐2 -­‐1 0 1 2 3 4

0 1 2 3 4 5 6 7 8 9 10

0 5 10 15 20 25

Z  distribu>on    

Z2  distribu>on    

Z4  distribu>on    

Solve  For  Price    18  

 dwσdtμ                      

 dwσdt2σμ                      

dwSσS1        dtS)σ

S1(

210Sμ

S1                        

dwSσS

ln(S)    dtSσSln(S)

21

tlnSSμ

Sln(S)    dln(S)

2*

222

*

222

2*

⋅+⋅=

⋅+⋅⎟⎟⎠

⎞⎜⎜⎝

⎛−=

⋅⋅+⋅⎟⎠⎞

⎜⎝⎛ ⋅−++⋅⋅=

⋅⋅∂

∂+⋅⎟⎟

⎞⎜⎜⎝

⎛⋅

∂⋅+

∂+⋅

∂=

dwSσSFdtSσ

SF

21

tFSμ

SFdF 22

2

2* ⋅⋅

∂+⋅⎟⎟

⎞⎜⎜⎝

⎛⋅⋅

∂⋅+

∂+⋅⋅

∂=

( )SlnF =

Price  differen>al  eqn  

This  differen>al  equa>on  cannot  be  solved  analy>cally,  but    can  be  solved  under  a  change  of  variable,  S.    Ln(S)  can  be  solved  for    

.

Solu>on  For  Price    19  

[ ]

[ ]t

2σμ

0tμ

0t

tσ  ,  tμNt

tσz    tμt

tσz    tμtt

2

*

*

0

*

0

t

eSeSSE

 eS~          S

eS      S

eS      S

⋅⎟⎟⎠

⎞⎜⎜⎝

⎛+

⋅⋅⋅

⋅⋅+⋅⋅

Δ⋅⋅+Δ⋅⋅Δ+

⋅=⋅=

=

=

[ ]

t2σμ

0tμ

0t

2

0

t

0

t

0t

ttt

2*

eSeS]M[S

tt,μN~SS

ln

tσztμSS

ln

tσztμ)ln(S)ln(S

tσztμ)ln(S)ln(S

⋅⎟⎟⎠

⎞⎜⎜⎝

⎛−

Δ+

⋅=⋅=

⋅σ⋅⎟⎟⎠

⎞⎜⎜⎝

⋅⋅+⋅=⎟⎟⎠

⎞⎜⎜⎝

⋅⋅+⋅+=

Δ⋅⋅+Δ⋅+=

Log  and  Expecta>on  Operators    20  

[ ] tμ)ln(S)ln(SE

tμSS

lnE

tσztμSS

ln

0t

0

t

t0

t

⋅+=

⋅=⎥⎦

⎤⎢⎣

⎡⎟⎟⎠

⎞⎜⎜⎝

⋅⋅+⋅=⎟⎟⎠

⎞⎜⎜⎝

⎛ [ ]

[ ]( ) ( ) tμSlnSEln

eSS

E

eSSE

*t

tμt

tμ0t

0

*

0

*

⋅+=

=⎥⎦

⎤⎢⎣

⋅=

[ ]( ) [ ]

[ ]( ) [ ] ( )

[ ]( ) [ ])ln(SE    SEln

 2tσ                                                                    

tμ-­‐μ)ln(SESEln

tμ)ln(SEtμSEln

tt

2

*tt

t*

t

>

⋅=

⋅=−

⋅+=⋅+

2σμμ

2σμμ

2*

2*

=−

+=

Note  nonlinearity  of  expecta>on  and  natural  log      Start  with  natural  log  of  price,    Start  with  price  expecta>on,      then  take  expected  value        then  take  natural  log    

Page 6: Dynamic equity price pdf

8/28/14  

Dynamic  Equity  Models   6  

Simula>on:  Probability  of  Median  and  Mean  Price    

21  

[ ] %4995.0SSPr

0011.0      1.12

1.0.12$40.00$45.09ln

T

TSSln

z

MEDT

0

MEDT

0

=<

−=⋅

⋅−⎟⎠

⎞⎜⎝

=⋅σ

⋅µ−⎟⎟⎠

⎞⎜⎜⎝

=

[ ] %071.54SSPr

1022.0      1.12

1.0.12$40.00$45.91ln

T

TSSln

z

EXPT

0

EXPT

0

=≤

=⋅

⋅−⎟⎠

⎞⎜⎝

=⋅σ

⋅µ−⎟⎟⎠

⎞⎜⎜⎝

=

Simula>on:  Probability  of  Min  and  Max  Price    22  

[ ] %013.SSPr

6547.3      1.12

1.0.12$40.00$23.95ln

T

TSSln

z

MINT

0

minT

0

=≤

−=⋅

⋅−⎟⎠

⎞⎜⎝

=⋅σ

⋅µ−⎟⎟⎠

⎞⎜⎜⎝

=

[ ] %001.SSPr

2347.4      1.12

1.0.12$40.00$93.91ln

T

TSSln

z

MAXT

0

MAXT

0

=≤

=⋅

⋅−⎟⎠

⎞⎜⎝

=⋅σ

⋅µ−⎟⎟⎠

⎞⎜⎜⎝

=

Probability  of  a  Price  Decline    23

16064.4      52125.0

52108.

21.10175.87ln

TμSSln

z 0

T

0

−=

⋅−⎟⎠⎞

⎜⎝⎛

=⋅

⋅−⎟⎟⎠

⎞⎜⎜⎝

=

Using  the  IBM  equity  price  sta>s>cs  of  µ=8%  and  σ  =  25%  (Topic  9)  ,  what  was  the  probability  of  the  drop  in  IBM  price  during  the  week  ending  October  10,  2008?    IBM  stock  opened  Monday  October  6th  at  $101.21,  ST,    and  closed  Friday  October  10th  at  $87.75,  S0.      Recall  that  the  IBM  return  sta>s>cs  were  computed  from  January  1962  to  September  2008.    

That  weekly  decline  was  expected  once  in  1,212  years      

[ ] %00159.)16064.4(N~)z(N~SSPr 00T =−==≤

[ ]( )0

0T

zN~SSPr =≤

Probability  of  Not  Exceeding  a  Cri>cal  Value    24  

An  investor  owns  100  shares  of  an  equity  with  a  current  price  per  share  of  $40.00.    The  equity  has  an  expected  rate  of  return  µ*=16%  and  annual  standard  devia>on    σ  =  20%.      What  is  the  probability  that  the  investor’s  $4,000,  S0,  will  grow  to  no  more  than  $6,000,  K,    aZer  5  years?        

14.0%    2

20%16.0%  2σμμ

22* =−=−=

[ ] %51.25)0.65860(N~)z(N~KSPr

0.65860      5.0.2

5.0.14$4,000$6,000ln

T

TSKln

z

0T

00

=−==≤

−=⋅

⋅−⎟⎠

⎞⎜⎝

=⋅σ

⋅µ−⎟⎟⎠

⎞⎜⎜⎝

=

[ ]( )0

T

zN~KSPr =≤ [ ]

( )2T

zN~KSPr =>

Page 7: Dynamic equity price pdf

8/28/14  

Dynamic  Equity  Models   7  

Probability  of  a  Loss  of  Value      25  

What  is  the  probability  that  the  investor  will  have  a  loss  aZer  5  years?  (  S0  =  K  =  $4,000  )    

The  probability  of  a  loss  is  5.88%  

[ ] 5.88%1.56525)(N~)(zN~KS  Pr

1.56525      5.0.2

5.0.14$4,000$4,000ln

TμSKln

z

0T

00

=−==≤

−=⋅

⋅−⎟⎠

⎞⎜⎝

=⋅

⋅−⎟⎟⎠

⎞⎜⎜⎝

=

[ ]( )0

T

zN~KSPr =≤ [ ]

( )2T

zN~KSPr =>

Probability  of  Exceeding  a  Cri>cal  Value    26  26  

An  investor  owns  100  shares  of  an  equity  with  a  current  price  per  share  of  $40.00.    The  equity  has  an  expected  rate  of  return  µ*=16%  and  annual  standard  devia>on    σ  =  20%.      What  is  the  probability  that  the  investor’s  $4,000,  S0,  will  grow  to  more  than  $6,000,  K,  aZer  5  years?        

The  probability  that  the  value  of  the  shares  exceeds  $6,000  is  74.49%                    

[ ] %49.74)Z(N~)Z(N~)Z(N~1KSPr 200T ==−=−=>

( )

0.65860                                                                                                      5.0.2

5.0.14$6,000$4,000ln

Tσ5.μKSln

Z

2*0

2

=⋅

⋅+⎟⎠

⎞⎜⎝

=⋅

⋅⋅−+⎟⎠⎞

⎜⎝⎛

0.65860      5.0.2

5.0.14$4,000$6,000ln

TμSKln

Z 00

−=⋅

⋅−⎟⎠

⎞⎜⎝

=⋅

⋅−⎟⎟⎠

⎞⎜⎜⎝

= [ ]( )0

T

zN~KSPr =≤ [ ]

( )2T

zN~KSPr =>

Simple  Binary  Op>on    27  

A  security,  C,  is  offered  as  follows:        If  an  equity,  S,  currently  priced  at  $40,  S0,  exceeds  $45,  $K,  aZer  one  year  (T=1.0),  then  the  buyer  of  this  security,  C,  will  receive  $K,  if  the  equity,  S,    is  less  than  or  equal  to  K,  then  the  buyer  will  receive  nothing.    The  annual  standard  devia>on  of  the  equity,  σ,  is  20%  and  the  annual  expected  risk  free  rate  of  return,  r*,  is  6%.    If  ST  >  K,  then  CT  =  K  If  ST  ≤  K,  then  CT  =  0    

[ ] ( )( )

78.14$34867.45$e                    

.38892-­‐N~45$e                    

dN~KeCEeC

06.

106.

2Tr

TTr

0

**

=⋅⋅=

⋅⋅=

⋅⋅=⋅=

⋅−

⋅−⋅−

( )

( )38892.  

12.

12..5.064540ln

         

Tσ.5rKSln

d

2

2*0

2

−=⋅

⋅⋅−+⎟⎠⎞

⎜⎝⎛

=

⋅⋅−+⎟⎠⎞

⎜⎝⎛

=

[ ] [ ]( )2

TT

dN~K                    

KSPrKCE

⋅=

>⋅=

The  fair  value  of  this  security  known  as  a  “cash  or  nothing  call  op>on”  is  $14.78  

[ ]( )0

T

dN~KSPr =≤ [ ]

( )2T

dN~KSPr =>

Confidence  Intervals    28  

$32.84          e$40.00          

eSS

$57.17          e$40.00          

eSS

0.50.21.959960.5.16

Tσ1.95996TμT

0.50.21.959960.5.16

Tσ1.95996TμT

*

0

*

0

=

=

=

=

=

=

⋅⋅−⋅⋅

⋅⋅−⋅⋅

⋅⋅+⋅⋅

⋅⋅+⋅⋅

+

Confidence  Level  (1-­‐α)

α α/2 -­‐Z +Z

90% 10% 5.00% -­‐1.64485 1.6448595% 5% 2.50% -­‐1.95996 1.9599699% 1% 0.50% -­‐2.57583 2.57583

What  are  the  upper  and  lower  bounds  on  a  future  stock  price  for  which  one  is  95%  (=1-­‐α)  confident?    St+  and  St-­‐  are  the  upper  and  lower  bounds  at  >me  T  =  0.5  years    

( )95996.1N~ −

Page 8: Dynamic equity price pdf

8/28/14  

Dynamic  Equity  Models   8  

Value  at  Risk  (VaR)    29  

What  is  the  maximum  loss  that  an  investor  would  expect  over  some  >me  period  t  ?        For  example,  what  is  the  maximum  loss  expected  with  95%  confidence    from  owning  an  equity  over  a  10  day  period?    The  equity  has  µ*=  16%,  σ  =  20%,  and  S0  =  $40.00.    Unlike  the  confidence  interval,    which  uses  a  two  tailed  confidence  ,  VaR  is  a  one-­‐tail  interval.            

Confidence  Level  (1-­‐α)

α -­‐Z

90% 10% -­‐1.2815595% 5% -­‐1.6448599% 1% -­‐2.32635

70.37$          e00.40$          

eSS

252102.01.64485

2521016.

Tσ1.64485TμT

*

0

=

=

=

⋅⋅−⋅⋅

⋅⋅−⋅⋅−

( )64485.1N~ −

Value  at  Risk  (VaR)    30  

The  minimum  95%  confident  price  is  $37.67,  thus  the  95%  maximum  expected  loss  is  $3.63  or  value  at  risk,  VaR    

   And  commonly  approximated  for  short  >me  periods  as  follows    

$5.6634.34$00.40$VaR =−=

( )

$2.30                

e100.40$                

e1SVaR

252102.01.64485

2521016.

TσzTμ0

*

=

⎟⎟

⎜⎜

⎛−⋅=

−⋅=

⋅⋅−⋅

⋅⋅+⋅

$2.54                

e100.40$                

e1SVaR

252102.01.64485

0

TσzT*μ

=

⎟⎟

⎜⎜

⎛−⋅=

⎟⎠⎞⎜

⎝⎛ −⋅=

⋅⋅−

⋅⋅+⋅

   VaR    is  computed  directly  as  follows    

Expected  Value  Exceeding  Cri>cal  Value  31  

The  same  problem  as  last  slide,  but  now  -­‐  what  is  the  expected  value  of  the  equity  posi>on  given  that  the  cri>cal  value,  K,  has  been  exceeded?        

[ ] [ ] ( )( )

( )( )2

1Tμ0

2

1TTT

zN~zN~eS                                              

zN~zN~SEKS|SE

*

⋅⋅=

⋅=>

( )

( )Tσ

Tσ5.μKSln

z

Tσ5.μKSln

z

2*0

2

2*0

1

⋅⋅−+⎟⎠⎞

⎜⎝⎛

=

⋅⋅++⎟⎠⎞

⎜⎝⎛

=

0.658605.0.2

5.0.14$6,000$4,000ln

z

10581.15.0.2

5.0.18$6,000$4,000ln

z

2

1

=⋅

⋅+⎟⎠

⎞⎜⎝

=

=⋅

⋅+⎟⎠

⎞⎜⎝

=

[ ]

344,10$                                                                  074492.086560.16.8902$                                                                  

074492.086560.e000,4$000,6$S|SE 516.

TT

=

⋅=

⋅=> ⋅

The  deriva>on  details  are  not  included  in  this  course.    

0

0.002

0.004

0.006

0.008

0.01

0.012

0.014

$0 $20 $40 $60 $80 $100 $120 $140 $160 $180 $200

Example:  Price  Distribu>on  at  >me  T  (5Yrs)    32  

[ ]

[ ]447214.  ,  .3888794N

Tσ  ,  Tμ)ln(SNT

e~        

e~S 0 ⋅⋅+

K=$60  

E[ST]=$89.02  

Median[ST]=$80.55  

E[ST|ST>K]=$103.44  

Mode[ST]=$65.95  

S0  

Page 9: Dynamic equity price pdf

8/28/14  

Dynamic  Equity  Models   9  

Another  Simple  Binary  Op>on    33  

A  security,  C,  is  offered  as  follows:        If  an  equity  currently  priced  at  $40,  S0,  exceeds  $45,  K,  aZer  exactly  one  year  (T=1.0),  then  the  buyer  of  this  security  will  receive  the  price  of  the  equity,  ST,  if  the  equity,  S,  is  less  than  or  equal  to  K,  then  the  buyer  will  receive  nothing.    If  ST  >  K,  then  CT  =  ST  If  ST  ≤  K,  then  CT  =  0    

[ ]( ) ( )

00.17$42509.40$          .18892-­‐N~40$  dN~S          

CEeC

10

TTr

0

*

=⋅=

⋅=⋅=

⋅= ⋅−

[ ] [ ] [ ]

( ) [ ] ( )( )

( )1Tr0

2

1T2

TTTT

dN~eS                      

dN~dN~SEdN~                    

KS|SEKSPrCE

*

⋅⋅=

⋅⋅=

>⋅>=

⋅ The  fair  value  of  this  security  known  as  a  “asset  or  nothing  call  op>on”  is  $14.78  

( )

( )18892.  

12.

12..5.064540ln

         

Tσ.5rKSln

d

2

2*0

1

−=⋅

⋅⋅++⎟⎠⎞

⎜⎝⎛

=

⋅⋅++⎟⎠⎞

⎜⎝⎛

=

[ ]( )0

T

dN~KSPr =≤ [ ]

( )2T

dN~KSPr =>

0

0.01

0.02

0.03

0.04

0.05

$10 $20 $30 $40 $50 $60 $70 $80 $90

Comparing  the  Two  Binary  Op>ons    

¨  cash  or  nothing  call  op>on ¨  asset  or  nothing  call  op>on 34

[ ] [ ] [ ]

( ) [ ] ( )( )

( )

[ ]( )10

Tr

0

1Tr

0

2

1T2

TTTT

dN~S                      

CEe              C

dN~eS                      

dN~dN~SEdN~                    

KS|SEKSPrCE

T*

*

⋅=

⋅=

⋅⋅=

⋅⋅=

>⋅>=

⋅−

[ ] [ ]( )

[ ]

( )2Tr0

T

2

TT

dN~KeC

KS|KEK

dN~K                    

KSPrKCE

*

⋅⋅=

>=

⋅=

>⋅=

⋅−

[ ]( ) ( )20

T

d-­‐N~dN~KSPr

=

=≤ [ ]( )2

T

dN~KSPr =>

KST >KST ≤

[ ]KS|SE TT >

K

Essen>al  Concepts    

 

35  

Appendix:  Probability  and  Expecta>on  Summary  36  

[ ]( ) ( ) ( )

[ ] [ ] ( )( )

[ ] ( )

[ ] [ ] ( )( )2

1TTT

2T

2

1TTT

002

T

dN~dN~SEKS|SE

dN~KSPr

zN~zN~SEKS|SE

zN~1z-­‐N~zN~KSPr

⋅=>

=>

⋅=>

−==

=>[ ]( ) ( )

( )

[ ]( )2

T

2

20

T

d-­‐N~KSPr

zN~1

z-­‐N~zN~KSPr

=≤

−=

=

=≤

Risk  Neutral  

Risk  Neutral  

[ ][ ]    E    Pr Risk  neutral  probability  

Risk  neutral  expecta>on  

Page 10: Dynamic equity price pdf

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Dynamic  Equity  Models   10  

Appendix:  1  Tail  Confidence    37  

90%                                                                                                      95%                                                                                                    99%  Confidence  

95%  confident  that  return  rate  lies  above  the  shaded  area    

Appendix:  2  Tail  Confidence    38  

90%                                                                                                      95%                                                                                                    99%  Confidence  

95%  confident  that  return  rate  lies  between  the  shaded  areas