4/5/14

Modeling share prices: Bank of America to hold


Here we introduce a new pricing model for Bank of America (NYSE: BAC). We have been trying to build a reliable model for BAC since 2008. Price modeling is based on our concept of stock pricing as a decomposition of a share price into a weighted sum of two consumer price indices (CPIs). The background idea is a simplistic one: there is a potential trade-off between a given share price and goods&services the company produces/provides. It is well known that the energy consumer price does influence the price of energy companies. In this study, we express the influence of various goods and services by related consumer price index. For example, the influence of energy is expressed by consumer price index of energy. 

One CPI is not enough, however. Any company competes with all other companies on the market. Therefore, the influence of the driving CPI on the company’s stock price also depends on the competitive power of all other CPIs. In our model, the net change in market prices is expressed by one reference CPI. This CPI represents the dynamics of price environment. Hence, the pricing model has to include two defining CPIs.  

The model searches for driving and reference CPIs. The BLS reports the estimates for hundreds CPIs, but we have selected only 92 representatives for our study (see Appendix). The selected CPIs include all major categories as well as quite a few minor subcategories. To obtain two defining CPIs, we use linear regression of a given stock price on all pairs of 92 CPIs. The defining CPIs may lead the modeled price or lag behind it because of possible time delays between action and reaction (the time needed for any price changes to pass through). The model includes such delays (up to +-11 months) for both CPIs. Thus, the number of tested models for each stock approaches 1 million and only one is selected. 

Bank of America was included in our study of bankruptcy cases in the USA. The initial model was not stable and the prediction for 2009 - 2011 was not fully correct.  In March 2012, we presented a model for monthly closing (adjusted for splits and dividends) price based on two consumer price indices: other food at home (OFH) and housing (H). This intermediate model was also biased. In December 2012, we published a paper comparing BAC with four financial companies and revised the previously obtained model. The model estimated in December 2012 includes the index of food away from home (SEFV) and the index of rent of shelter (RSH).  

Here we update the last model using new data between December 2012 and March 2014. The December 2012 model has not changed. Table 1 lists defining parameters for BAC between March and October 2012, and from August 2013 to March 2014. For each month, the best (from 1 million) model is based on the same defining CPIs – the index of food away from home (SEFV) and the index of rent of shelter (RSH).  In all cases, the lags are the same: zero and one month, respectively. Other coefficients and the standard error suffer just slight oscillations or drifts. 

Figure 1 depicts the overall evolution of both involved consumer price indices: SEFV and RSH, as well as those for the previous model: OFH and H. There are some differences between two pairs of defining CPIs which result in the change of the best fit model in March 2012. It is worth noting that these differences become prominent in 2011/2012 (OFH vs. SEFV). Before 2011, the relevant CPIs are similar and this might be the reason of the wrong model selection in 2012.  

The best-fit models for BAC(t) in March 2014 and December 2011 are as follows:

BAC(t) = -5.54SEFV(t-0) + 2.43RSH(t-1) + 19.49(t-2000) + 431.49, March 2014
 BAC(t) = -2.31OFH(t-0) +1.12H(t-0) + 2.18(t-2000) + 167.83, December 2011     

The price of BAC share is relatively well defined by the behaviour of the two defining CPI components. Figure 2 also depicts the high and low monthly prices for the same period, which illustrate the intermonth variation of the share price. These prices might be considered as natural limits of the monthly price uncertainty associated with the quantitative model. Figure 3 demonstrates the failure of the March 2012 model to predict the future of BAC price. The current model is valid since March 2012 (25 months is a row) and thus is more reliable than the previous one. Figure 4 displays the residual error which has standard deviation $2.86 for the period between July 2003 and March 2014. This is the uncertainty of the model for the future predictions. 

From Figure 2, BAC price is approximately $20 in April 2014.

Table 1. The monthly models for BAC for eight months in 2012 and for seven months in 2014/2013.

Month
C1
t1
b1
C2
t2
b2
c
d
 
2012
October
-5.9217
SEFV
0
2.6567
RSH
2
20.7381
447.5626
September
-5.8865
SEFV
0
2.6484
RSH
2
20.5481
443.7352
August
-5.8953
SEFV
0
2.6542
RSH
2
20.5659
444.0072
July
-5.9408
SEFV
0
2.6744
RSH
2
20.7368
447.1716
June
-5.9322
SEFV
0
2.6797
RSH
2
20.6401
444.8138
May
-5.9688
SEFV
0
2.691
RSH
2
20.8133
448.3051
April
-5.9683
SEFV
0
2.6962
RSH
2
20.7737
447.2148
March
-5.9487
SEFV
0
2.6875
RSH
2
20.6911
445.9155
 
2014
and
2013
March
-5.5413
SEFV
0
2.427
RSH
1
19.4879
431.4925
February
-5.5254
SEFV
0
2.4246
RSH
1
19.41
429.3975
January
-5.5957
SEFV
0
2.4457
RSH
1
19.7611
436.0936
December
-5.6127
SEFV
0
2.4501
RSH
1
19.8513
437.8585
November
-5.6308
SEFV
0
2.4526
RSH
1
19.9578
440.1902
October
-5.6509
SEFV
0
2.4575
RSH
1
20.0682
442.3
September
-5.6788
SEFV
0
2.4623
RSH
1
20.2354
445.6533

 

Figure 1. Evolution of defining pairs: OFH/H vs. SEFV/RSH.

Figure 2. Observed and predicted BAC share prices based on SEFV/RSH

Figure 3. Observed and predicted BAC share prices based on OFH/H, as estimated in December 2011.

Figure 4. Model residuals, standard error of the model $2.86. 

 
Appendix. 92 defining CPIs  

CPI
CPI
C
headline CPI
M
medical care
F
food and beverages
MCC
medical care commodities
FB
food
PDRUG
prescription drugs
FH
food at home
MCS
medical care services
MEAT
meats, poultry, fish and eggs
MPRS
medical professional services
FISH
fish and seafood
HOSP
hospital and related services
DAIRY
dairy and related products
R
receration
FRUIT
fruits and vegetables
VAA
video and audio
NAB
nonalcoholic beverages
PETS
pets, pet products and services
OFH
other food at home
SPO
sporting goods
SEFV
food away from home
FOTO
photography
AB
alcoholic beverages
ORG
other recreational goods
H
housing
RS
recreation services
SH
shelter
RRM
recreational reading materials
RPR
rent of primary residence
EC
education and communication
ORPR
owners'  equivalent rent of residence
ED
education
THI
tenants' and household insurance
BOOK
educational books and supplies
FU
fuels and utilities
TUIT
tuition, other school fees, and child care
HHE
household energy
CO
communication
HFO
household furnishing and operations
POST
postage and delivery services
FAB
furniture and bedding
INF
information and information processing
APL
appliances
IT
information technology, hardware and software
OHEF
other household equipment and furnishing
O
other goods and services
THOES
tools hardware equipment and supplies
TOB
tobacco and smoking products
HOS
housekeeping supplies
PC
persocal care
HO
household operations
PCP
personal care products
A
apparel
PCS
personal care  services
MAP
men's and boy's apparel
MISS
miscellaneous  personal services
WAP
women's and girl's apparel
LS
legal services
FOOT
footware
FS
financial services
BABY
infant's apparel
MISG
miscellaneous  personal goods
JEW
jewelry and watches
CM
CPI less medical care
T
transportation   
CE
CPI less energy
TPR
private transportation
CF
CPI less food
NUMV
new and used motor vehicles
CC
core CPI
NMV
new vehicles
CSH
CPI less shelter
NC
new cars
COMM
commodities
MF
motor fuel
DUR
durables
MVP
motor vehicle parts and equipment
E
energy
MVR
motor vehicle maintenance and repair
NDUR
nondurables
MVI
motor vehicle insurance
OS
other services
MVF
motor vehicle fees
RSH
rent of shelter
TPU
public transportations
SERV
services
AIRF
airline fare
TS
transportation services
OIT
other intercity transportation
CFSH
CPI less food and shelter
ITR
intracity transportation
CFSHE
CPI less food, shelter and energy

 

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