Analyzing Oil Futures with a Dynamic Nelson-Siegel Model...
Transcript of Analyzing Oil Futures with a Dynamic Nelson-Siegel Model...
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Department of Economics and Business
Aarhus University
Fuglesangs AllΓ© 4
DK-8210 Aarhus V
Denmark
Email: [email protected]
Tel: +45 8716 5515
Analyzing Oil Futures with a Dynamic Nelson-Siegel Model
Niels S. Hansen and Asger Lunde
CREATES Research Paper 2013-36
mailto:[email protected]
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Analyzing Oil Futures with a Dynamic Nelson-Siegel
Modelβ
Niels S. Hansenβ β‘ Asger Lundeβ Β§
Abstract
In this paper the dynamic Nelson-Siegel model is used to model the termstructure of futures contracts on oil and obtain forecasts of prices of thesecontracts. Three factors are extracted and modelled in a very flexible frame-work. The outcome of this exercise is a class of models which describes theobserved prices of futures contracts well and performs better than conven-tional benchmarks in realistic real-time out-of-sample exercises.Keywords: Oil futures, Nelson-Siegel, Normal Inverse Gaussian, GARCH,Copula.JEL classification: G17, C32, C53.
βWe acknowledge the support from CREATES, Center for Research in Econometric Analysis of TimeSeries (DNRF78), funded by the Danish National Research Foundation. Comments from participants ofthe Conference of Energy Finance 2012 in Trondheim and the CREATES seminar series are highly appre-ciated. We are grateful for the comments from Thomas Quistgaard Pedersen and for the comments fromtwo anonymous referees which have improved the quality of the paper significantly.
β Department of Economics and Business, School of Business and Social Sciences, Aarhus Universityand CREATES. Fuglesangs AlleΜ 4, DK-8210 Aarhus V.
β‘Corresponding author, e-mail: [email protected], phone: (45) 8716 5285.Β§Associate Member at Oxford-Man Institute of Quantitative Finance
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1 Introduction
In the aftermath of the financial crisis commodity markets have received a lot of at-
tention. Caballero et al. (2008) argue that commodity markets presented a more reliable
and attractive form of investment when the financial crisis spread throughout the finan-
cial markets. The growth in economic activity in Brazil, Russia, India and China has,
according to Geman (2005), contributed to the increased popularity and to increased
prices across commodity markets. Predicting prices of commodity futures contracts is
very interesting from an academic perspective and very valuable for producers, spec-
ulators and risk managers. We analyze a large dataset consisting of prices and time
to maturity of futures contracts on oil. We focus on oil because it is the most traded
commodity in the world. It is used in the production of many products most impor-
tantly for petroleum. Oil also serves as an important indicator for the overall state of the
world economy. In this paper we take on some of the challenges presented by data from
commodity markets. We obtain very valuable insights about the prices of commodity
futures and how to forecast them.
The objective in this paper is to develop a class of models which explains data well
and performs well out of sample. This paper makes several contributions. First, we
show that the dynamic Nelson-Siegel model can be used to extract a set of underlying
factors which describe the prices of futures contracts on oil. Second, we model the fac-
tors using the class of GARCH models with Normal Inverse Gaussian innovations in
a very flexible copula framework. Third, we successfully forecast the prices of futures
contracts on oil based on both a conventional mean squared error criterion and a direc-
tional criterion. Finally, we show how our model can be used to calculate value at risk
for portfolios consisting of the factors.
Several papers consider the modelling of oil futures. The traditional approach is to
specify a model for the underlying spot price and derive a term structure for futures
prices based on a no arbitrage argument, see Schwartz (1997) and Geman (2005) for
examples. In this paper we do not consider spot prices or their relationship to the
prices of futures contracts. We focus exclusively on modelling and forecasting the term
structure of futures contracts.
The data in this market, as well as data from other commodity markets, has a struc-
ture which resembles data from fixed income markets. Therefore models from the fixed
income literature, in particular interest rate models, are often applied to analyze com-
modity futures contracts. In this paper we apply a classical interest rate model to prices
of oil futures. The model is the dynamic Nelson-Siegel model, Nelson and Siegel (1987)
and Diebold and Li (2006), and the modelling approach is inspired by Noureldin (2011).
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The analysis is based on the assumption that the relationship between futures prices
and time to maturity can be described by three latent factors. The validity of this
assumption will be determined by how well our models perform out of sample. By
focussing the analysis on these factors the dynamic Nelson-Siegel model allows for a
substantial dimension reduction which facilitates the analysis. The dynamic Nelson-
Siegel model is also used with great success in areas other than yield curve modelling,
see for example Chalamandaris and Tsekrekos (2011) and Guo et al. (2014) where im-
plied volatility is modelled in this framework. In the commodity literature West (2011)
uses the dynamic Nelson Siegel model to estimate futures prices for long dated con-
tracts on agricultural products. The methodology is, however, different from the one
we apply. West (2011) relies on different versions of the Nelson-Siegel model to take
seasonality and other features into account. Instead we estimate the latent factors and
obtain multivariate time series. The idea is then to model and forecast these factors in
order to forecast futures prices. We show that models based on the dynamic Nelson-
Siegel model performs well in realistic real-time exercises as forecasting and value at
risk analysis.
Using techniques from the copula framework in Patton (2009) and Patton (2012), we
apply a decomposition which allows us to model three univariate time series and a de-
pendence structure individually. We may then draw on the vast literature on modelling
of univariate time series. In particular, the very flexible class of Normal Inverse Gaus-
sian GARCH (NIG-GARCH) models presented in Jensen and Lunde (2001), is shown
to describe the data well and at the same time offer accurate forecasts of the factors. We
consider two different models for the dependence..
We leave out a part of our sample for real-time forecast evaluation. In this period
we forecast the factors and hence the term structure of futures prices using our model
and compare the results to two other models. We show that we forecast more precisely
than our benchmarks in terms of mean squared error. Practitioners may not, however,
be interested in the mean squared error of a model but rather the models ability to
accurately predict the direction of the changes of the futures prices. We carry out an
analysis to investigate this desirable property of the different models. Finally, we show
that portfolios of oil futures can be constructed from the estimated factors and that we
can successfully calculate value at risk for these portfolios in our framework.
The rest of this paper is organized as follows. In section 2 we provide a thorough
description of the data set analyzed in this paper. Section 3 contains a description of the
model. In section 4 we present the results of the in-sample analysis. Section 5 contains
the results of the out-of-sample forecast analysis. Section 6 is devoted to the calculation
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and backtesting of value at risk. Finally, some concluding remarks are presented in
section 7.
2 Data
Data from the markets for commodity futures contracts is very different from many
other financial data sets. The unique features of the data make analyzing and fore-
casting challenging tasks. This section serves to illustrate the features of the data and
highlight potential challenges which we have to overcome.
The data set we consider consists of daily closing prices of monthly futures contracts
on oil from Reuters.1 The contracts are on light sweet crude oil (WTI), more details can
be found on the CME Group homepage.2 Every day a number of futures with different
time to maturity are traded. The maturities are approximately one month apart. Each
contract expires on the third trading day prior to the 25th calendar day in the month
before delivery. The first observations are from June 1st 2000 and the sample ends on
December 31st 2012 meaning that our sample consists of 55.123 observations of prices
and maturities.
It is important to understand the nature of the data in order to understand the prob-
lems we face in this paper. In order to grasp the structure and complexities of the data
it is useful to consider an example of actual data. In Table 1 we have presented a small
example of what the data looks like. This is only a very brief example, but there are sev-
eral important things to notice. First, note that only a limited number of contracts exists
on a given day. Consider for example the first row of the table, on this day a contract
with 495 days to delivery does not exist. Such a contract exists on the next day, though.
Secondly, the data contains a number of holes. On 06.09.2010 it was possible to trade
in a contract with 494 days to maturity, but no one did. This means that we have two
kinds of holes in the data set contracts that do not exist and contracts which exist but are
not traded. Both pose problems for a traditional time series analysis which is not well
suited for dealing with situations in which the number of observations changes from
day to day. Assume now that on 06.10.2010 we are interested in forecasting the price of
a contract with 492 days to delivery which is potentially traded on 06.11.2010. Futures
contracts are characterized by their time to maturity, so a good way of forecasting is to
consider a time series of prices of contracts with the same time to maturity. Such a time
1The data is kindly provided by Oxford-Man Institute of Quantitative Finance and obtained fromThomson Reuters Tick History with help from Kevin Sheppard.
2http://www.cmegroup.com/trading/energy/crude-oil/light-sweet-crude_contract_
specifications.html
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http://www.cmegroup.com/trading/energy/crude-oil/light-sweet-crude_contract_specifications.htmlhttp://www.cmegroup.com/trading/energy/crude-oil/light-sweet-crude_contract_specifications.html
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Table 1: Data example.
Price (time to maturity (trading days))Contract name 2012M 2012Z 2013M 2013Z 2014Z
06.07.2010 . . . 81.50 (496) 82.48 (622) - 85.00 (875) 85.65 (1127) . . .06.08.2010 . . . 81.37 (495) 83.10 (621) 83.70 (746) 84.60 (874) 86.22 (1126) . . .06.09.2010 . . . - 84.70 (620) - 85.95 (873) 87.60 (1125) . . .06.10.2010 . . . 83.70 (493) 85.60 (619) - 86.85 (872) 87.91 (1124) . . .
Example of actual data. A subsample of the prices and corresponding maturities for contracts tradedbetween 06.07.2010 and 06.10.2012 for five different contracts. The first part of the name for each contractis the year of delivery. The letter in the contract name denotes the month of delivery. M is June and Z isDecember.
series is not observed, but it could be constructed by interpolation, see Diebold and Li
(2006) or Noureldin (2011) for examples from the interest rate literature. Another possi-
bility is to consider the time series of prices for this particular contract, 2012M (delivery
in June 2012) and fit an autoregressive model. The drawbacks here are that the previous
observations of prices are based on another time to maturity. Furthermore, we have to
decide what to do about missing values. If the contract was introduced to the market
recently this approach might be infeasible due to the limited number of observations.
Note, that we always know the maturities of the contracts which are potentially traded
on the next day.
The model we apply in this paper is introduced by Diebold and Li (2006). They ap-
ply the model to monthly yields on U.S. Treasuries. We notice, that our data resembles
the data from their analysis. Therefore, we apply the same model to model the prices
of futures contracts on oil. Diebold and Li (2006) present the most important stylized
facts of the yield curve dynamics and argue that their model in theory should be able
to account for all these. We will argue, that the stylized facts presented by Diebold and
Li (2006) are all present in our current data set. Diebold and Li (2006) consider the five
following characteristics:
(1) The average yield curve is increasing and concave.
(2) The yield curve assumes a variety of shapes through time including upward slop-
ing, downward sloping, humped and inverted humped.
(3) Yield dynamics are persistent, and spread dynamics are much less persistent.
(4) The short end of the yield curve is more volatile than the long end.
(5) Long rates are more persistent than short rates.
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We are going to present our data set and adapt the above characteristics to our
framework and argue that prices of oil futures exhibit the same characteristics. To get
an idea of which contracts we have available, we first present a plot of the observed ma-
turities over time in Figure 1. Each dot in this plot indicates an observed price. Several
things are worth noticing. Generally it seems that we have a lot of observations in the
short end throughout the sample, while observations in the long end are more scarce.
Time to maturity is measured in business days. Up until 2007 we have observations
of contracts with maturities around 1700 days. From 2007 we have contracts with long
time to maturity around 2200 days. It seems that, for long maturities, trading is con-
centrated in contracts where maturities are about 12 months apart. This is represented
by the diagonal βlinesβ. Transactions for medium long maturities are concentrated in
contracts where maturity is 6 months apart. This can be seen as the diagonal lines are
closer to each other for maturities between 300 and 500 days.
Diebold and Li (2006) analyses a data set of monthly yields and fix maturities by
linear interpolation. This means that they analyze time series of 17 different contracts.
We do not use linear interpolation which means that we have different maturities on
different days. To enable a comparison of our data to the stylized facts we pool the
data into 23 groups such that we have all prices of contracts with less than 100 days
to maturity in the first group. Similarly all prices for contracts with 100 to 200 days to
maturity are collected in the next group and so on. This division into groups is only
used to highlight some of the stylized facts of Diebold and Li (2006) and not in the
actual analysis.
The first of the characteristics presented above corresponds to a situation in which
the average term structure of the futures contracts is increasing and concave. In the
top panel of Figure 2 we present the average term structure. Generally, prices are in-
creasing in maturity and it seems that averaged over time the term structure can be
approximated reasonably well by a smoothly increasing function. The fourth charac-
teristic states that the prices of contracts in the short end of the term structure are more
volatile than the prices of contracts in the long end. To investigate this, we take a look
at the standard deviation of the different maturities. In the middle panel of Figure 2 we
have the standard deviations of the prices of contracts with different maturities. We see,
that prices of contracts with short maturity are generally more volatile than contracts
with long maturities. The standard deviations are quite high for some contracts in the
medium range of time to maturity. Diebold and Li (2006) observes the same pattern.
In the lower panel in Figure 2 we have plotted the natural logarithm of the number of
observations for each group of maturities. Clearly, we have a fewer observations for
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