Option Pricing Revisited: The Role of Price Volatility and Dynamics
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DOI: 10.22004/ag.econ.343544
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- Shu-Ling Chen & John D. Jackson & Hyeongwoo Kim & Pramesti Resiandini, 2014.
"What Drives Commodity Prices?,"
American Journal of Agricultural Economics, Agricultural and Applied Economics Association, vol. 96(5), pages 1455-1468.
- Shu-Ling Chen & John D. Jackson & Hyeongwoo Kim & Pramesti Resiandini, 2010. "What Drives Commodity Prices?," Auburn Economics Working Paper Series auwp2010-05, Department of Economics, Auburn University.
- Chen, Shu-Ling & Jackson, John D. & Kim, Hyeongwoo & Resiandini, Pramesti, 2012. "What Drives Commodity Prices?," MPRA Paper 40711, University Library of Munich, Germany.
- Shu-Ling Chen & John D. Jackson & Hyeongwoo Kim & Pramesti Resiandini, 2013. "What Drives Commodity Prices?," Auburn Economics Working Paper Series auwp2013-03, Department of Economics, Auburn University.
- Robert J. Shiller, 2015. "Irrational Exuberance," Economics Books, Princeton University Press, edition 3, number 10421.
- Whaley, Robert E, 1986. "Valuation of American Futures Options: Theory and Empirical Tests," Journal of Finance, American Finance Association, vol. 41(1), pages 127-150, March.
- Schwert, G. William, 2003.
"Anomalies and market efficiency,"
Handbook of the Economics of Finance, in: G.M. Constantinides & M. Harris & R. M. Stulz (ed.), Handbook of the Economics of Finance, edition 1, volume 1, chapter 15, pages 939-974,
Elsevier.
- G. William Schwert, 2002. "Anomalies and Market Efficiency," NBER Working Papers 9277, National Bureau of Economic Research, Inc.
- Baruník, Jozef & Čech, František, 2021. "Measurement of common risks in tails: A panel quantile regression model for financial returns," Journal of Financial Markets, Elsevier, vol. 52(C).
- Markus K. Brunnermeier & Lasse Heje Pedersen, 2009.
"Market Liquidity and Funding Liquidity,"
The Review of Financial Studies, Society for Financial Studies, vol. 22(6), pages 2201-2238, June.
- Lasse Heje Pederson & Markus K Brunnermeier, 2007. "Market Liquidity and Funding Liquidity," FMG Discussion Papers dp580, Financial Markets Group.
- Brunnermeier, Markus K. & Pedersen, Lasse Heje, 2007. "Market liquidity and funding liquidity," LSE Research Online Documents on Economics 24478, London School of Economics and Political Science, LSE Library.
- Markus K. Brunnermeier & Lasse Heje Pedersen, 2007. "Market Liquidity and Funding Liquidity," NBER Working Papers 12939, National Bureau of Economic Research, Inc.
- Brunnermeier, Markus & Pedersen, Lasse Heje, 2007. "Market Liquidity and Funding Liquidity," CEPR Discussion Papers 6179, C.E.P.R. Discussion Papers.
- In Joon Kim & Sol Kim, 2005. "Is it important to consider the jump component for pricing and hedging short‐term options?," Journal of Futures Markets, John Wiley & Sons, Ltd., vol. 25(10), pages 989-1009, October.
- Jinji Hao & Jin E. Zhang, 2013. "GARCH Option Pricing Models, the CBOE VIX, and Variance Risk Premium," Journal of Financial Econometrics, Oxford University Press, vol. 11(3), pages 556-580, June.
- Hasbrouck, Joel, 1993. "Assessing the Quality of a Security Market: A New Approach to Transaction-Cost Measurement," The Review of Financial Studies, Society for Financial Studies, vol. 6(1), pages 191-212.
- David S. Bates, 2022. "Empirical Option Pricing Models," Annual Review of Financial Economics, Annual Reviews, vol. 14(1), pages 369-389, November.
- Cars Hommes & Anita Kopányi-Peuker & Joep Sonnemans, 2021.
"Bubbles, crashes and information contagion in large-group asset market experiments,"
Experimental Economics, Springer;Economic Science Association, vol. 24(2), pages 414-433, June.
- Cars Hommes & Anita Kopányi-Peuker & Joep Sonnemans, "undated". "Bubbles, crashes and information contagion in large-group asset market experiments," Tinbergen Institute Discussion Papers 19-016/II, Tinbergen Institute.
- Peter Christoffersen & Bruno Feunou & Yoontae Jeon & Chayawat Ornthanalai, 2021. "Time-Varying Crash Risk Embedded in Index Options: The Role of Stock Market Liquidity [Does realized skewness predict the cross-section of equity returns?]," Review of Finance, European Finance Association, vol. 25(4), pages 1261-1298.
- Robert C. Merton, 2005.
"Theory of rational option pricing,"
World Scientific Book Chapters, in: Sudipto Bhattacharya & George M Constantinides (ed.), Theory Of Valuation, chapter 8, pages 229-288,
World Scientific Publishing Co. Pte. Ltd..
- Robert C. Merton, 1973. "Theory of Rational Option Pricing," Bell Journal of Economics, The RAND Corporation, vol. 4(1), pages 141-183, Spring.
- Giovanni Barone Adesi & Robert F. Engle & Loriano Mancini, 2014.
"A GARCH Option Pricing Model with Filtered Historical Simulation,"
Palgrave Macmillan Books, in: Giovanni Barone Adesi (ed.), Simulating Security Returns: A Filtered Historical Simulation Approach, chapter 4, pages 66-108,
Palgrave Macmillan.
- Giovanni Barone-Adesi & Robert F. Engle & Loriano Mancini, 2008. "A GARCH Option Pricing Model with Filtered Historical Simulation," The Review of Financial Studies, Society for Financial Studies, vol. 21(3), pages 1223-1258, May.
- Fama, Eugene F, 1970. "Efficient Capital Markets: A Review of Theory and Empirical Work," Journal of Finance, American Finance Association, vol. 25(2), pages 383-417, May.
- Jian Li & Jean-Paul Chavas & Xiaoli L. Etienne & Chongguang Li, 2017.
"Commodity price bubbles and macroeconomics: evidence from the Chinese agricultural markets,"
Agricultural Economics, International Association of Agricultural Economists, vol. 48(6), pages 755-768, November.
- Li, Jian & Chavas, Jean-Paul & Etienne, Xiaoli & Li, Chongguang, 2016. "Commodity Price Bubbles and Macroeconomics: Evidence from Chinese Agricultural Markets," 2016 Annual Meeting, July 31-August 2, Boston, Massachusetts 235068, Agricultural and Applied Economics Association.
- Hull, John C & White, Alan D, 1987. "The Pricing of Options on Assets with Stochastic Volatilities," Journal of Finance, American Finance Association, vol. 42(2), pages 281-300, June.
- Koenker, Roger & Xiao, Zhijie, 2006. "Quantile Autoregression," Journal of the American Statistical Association, American Statistical Association, vol. 101, pages 980-990, September.
- Xinyue He & Teresa Serra, 2022. "Are price limits cooling off agricultural futures markets?," American Journal of Agricultural Economics, John Wiley & Sons, vol. 104(5), pages 1724-1746, October.
- Peter Fortune, 1996. "Anomalies in option pricing: the Black-Scholes model revisited," New England Economic Review, Federal Reserve Bank of Boston, issue Mar, pages 17-40.
- Jensen, Mads Vestergaard & Pedersen, Lasse Heje, 2016.
"Early option exercise: Never say never,"
Journal of Financial Economics, Elsevier, vol. 121(2), pages 278-299.
- Pedersen, Lasse Heje & Vestergaard Jensen, Mads, 2015. "Early Option Exercise: Never Say Never," CEPR Discussion Papers 11019, C.E.P.R. Discussion Papers.
- Isengildina-Massa, Olga & Irwin, Scott H. & Good, Darrel L., 2010. "Quantile Regression Estimates of Confidence Intervals for WASDE Price Forecasts," Journal of Agricultural and Resource Economics, Western Agricultural Economics Association, vol. 35(3), pages 1-23, December.
- Heston, Steven L & Nandi, Saikat, 2000. "A Closed-Form GARCH Option Valuation Model," The Review of Financial Studies, Society for Financial Studies, vol. 13(3), pages 585-625.
- Christoffersen, Peter & Jacobs, Kris & Ornthanalai, Chayawat, 2012. "Dynamic jump intensities and risk premiums: Evidence from S&P500 returns and options," Journal of Financial Economics, Elsevier, vol. 106(3), pages 447-472.
- Bige Kahraman & Heather Tookes, 2020. "Margin Trading and Comovement During Crises [Connected stocks]," Review of Finance, European Finance Association, vol. 24(4), pages 813-846.
- Peter H. Gruber & Claudio Tebaldi & Fabio Trojani, 2021. "The Price of the Smile and Variance Risk Premia," Management Science, INFORMS, vol. 67(7), pages 4056-4074, July.
- Stuart D. Frank & Scott H. Irwin & George H. Pfeiffer & Charles E. Curtis, 1989. "Further Evidence on Soybean Marketing Strategies: The Role of Options," Review of Agricultural Economics, Agricultural and Applied Economics Association, vol. 11(2), pages 213-219.
- Robert F. Stambaugh & Jianfeng Yu & Yu Yuan, 2015.
"Arbitrage Asymmetry and the Idiosyncratic Volatility Puzzle,"
Journal of Finance, American Finance Association, vol. 70(5), pages 1903-1948, October.
- Robert F. Stambaugh & Jianfeng Yu & Yu Yuan, 2012. "Arbitrage Asymmetry and the Idiosyncratic Volatility Puzzle," NBER Working Papers 18560, National Bureau of Economic Research, Inc.
- Nicholas Barberis & Lawrence J. Jin & Baolian Wang, 2021. "Prospect Theory and Stock Market Anomalies," Journal of Finance, American Finance Association, vol. 76(5), pages 2639-2687, October.
- Dabin Wang & William G. Tomek, 2007. "Commodity Prices and Unit Root Tests," American Journal of Agricultural Economics, Agricultural and Applied Economics Association, vol. 89(4), pages 873-889.
- Sushil Bikhchandani & Sunil Sharma, 2001. "Herd Behavior in Financial Markets," IMF Staff Papers, Palgrave Macmillan, vol. 47(3), pages 1-1.
- Christoffersen, Peter & Heston, Steve & Jacobs, Kris, 2006.
"Option valuation with conditional skewness,"
Journal of Econometrics, Elsevier, vol. 131(1-2), pages 253-284.
- Peter Christoffersen & Steve Heston & Kris Jacobs, 2003. "Option Valuation with Conditional Skewness," CIRANO Working Papers 2003s-50, CIRANO.
- Ornthanalai, Chayawat, 2014. "Lévy jump risk: Evidence from options and returns," Journal of Financial Economics, Elsevier, vol. 112(1), pages 69-90.
- Jian Li & Jean‐Paul Chavas, 2023. "A dynamic analysis of the distribution of commodity futures and spot prices," American Journal of Agricultural Economics, John Wiley & Sons, vol. 105(1), pages 122-143, January.
- Georges Dionne, 2013.
"Risk Management: History, Definition, and Critique,"
Risk Management and Insurance Review, American Risk and Insurance Association, vol. 16(2), pages 147-166, September.
- Dionne, Georges, 2013. "Risk management: History, definition and critique," Working Papers 13-2, HEC Montreal, Canada Research Chair in Risk Management.
- Georges Dionne, 2013. "Risk Management : History, Definition and Critique," Cahiers de recherche 1302, CIRPEE.
- Roger Koenker & Zhijie Xiao, 2004. "Unit Root Quantile Autoregression Inference," Journal of the American Statistical Association, American Statistical Association, vol. 99, pages 775-787, January.
- Jeff Fleming & Chris Kirby & Barbara Ostdiek, 2006. "Stochastic Volatility, Trading Volume, and the Daily Flow of Information," The Journal of Business, University of Chicago Press, vol. 79(3), pages 1551-1590, May.
- Barberis, Nicholas & Greenwood, Robin & Jin, Lawrence & Shleifer, Andrei, 2018.
"Extrapolation and bubbles,"
Journal of Financial Economics, Elsevier, vol. 129(2), pages 203-227.
- Nicholas Barberis & Robin Greenwood & Lawrence Jin & Andrei Shleifer, 2015. "Extrapolation and Bubbles," Working Paper 357401, Harvard University OpenScholar.
- Nicholas Barberis & Robin Greenwood & Lawrence Jin & Andrei Shleifer, 2016. "Extrapolation and Bubbles," NBER Working Papers 21944, National Bureau of Economic Research, Inc.
- Jondeau, Eric & Rockinger, Michael, 2003. "Conditional volatility, skewness, and kurtosis: existence, persistence, and comovements," Journal of Economic Dynamics and Control, Elsevier, vol. 27(10), pages 1699-1737, August.
- Black, Fischer & Scholes, Myron S, 1973. "The Pricing of Options and Corporate Liabilities," Journal of Political Economy, University of Chicago Press, vol. 81(3), pages 637-654, May-June.
- Andrew M. McKenzie & Michael R. Thomsen & Michael K. Adjemian, 2022. "Characterizing implied volatility functions from agricultural options markets," American Journal of Agricultural Economics, John Wiley & Sons, vol. 104(5), pages 1605-1624, October.
- Urcola, Hernan A. & Irwin, Scott H., 2011. "Are Agricultural Options Overpriced?," Journal of Agricultural and Resource Economics, Western Agricultural Economics Association, vol. 36(1), pages 1-15, April.
- Oleg Rytchkov, 2014. "Asset Pricing with Dynamic Margin Constraints," Journal of Finance, American Finance Association, vol. 69(1), pages 405-452, February.
- repec:bla:jfinan:v:59:y:2004:i:2:p:755-793 is not listed on IDEAS
- George A. Akerlof & Robert J. Shiller, 2010. "Animal Spirits: How Human Psychology Drives the Economy, and Why It Matters for Global Capitalism," Economics Books, Princeton University Press, edition 1, number 9163.
- Irwin, Scott H. & Pelly, Robert A. & Zulauf, Carl R., 1989. "An Investigation of Pricing Models for Live Cattle and Feeder Cattle Options," Staff Papers 232393, Virginia Polytechnic Institute and State University, Department of Agricultural and Applied Economics.
- Bakshi, Gurdip & Cao, Charles & Chen, Zhiwu, 1997.
"Empirical Performance of Alternative Option Pricing Models,"
Journal of Finance, American Finance Association, vol. 52(5), pages 2003-2049, December.
- Charles Quanwei Cao & Gurdip S. Bakshi & Zhiwu Chen, 1997. "Empirical Performance of Alternative Option Pricing Models," Yale School of Management Working Papers ysm65, Yale School of Management.
- Charles Quanwei Cao & Gurdip S. Bakshi & Zhiwu Chen, 1997. "Empirical Performance of Alternative Option Pricing Models," Yale School of Management Working Papers ysm54, Yale School of Management.
- Etienne, Xiaoli L. & Irwin, Scott H. & Garcia, Philip, 2014. "Bubbles in food commodity markets: Four decades of evidence," Journal of International Money and Finance, Elsevier, vol. 42(C), pages 129-155.
- Filip Žikeš & Jozef Baruník, 2015.
"Semi-parametric Conditional Quantile Models for Financial Returns and Realized Volatility,"
Journal of Financial Econometrics,
Society for Financial Econometrics, vol. 14(1), pages 185-226.
- Filip Zikes & Jozef Barunik, 2013. "Semiparametric Conditional Quantile Models for Financial Returns and Realized Volatility," Papers 1308.4276, arXiv.org.
- Žikeš, Filip & Baruník, Jozef, 2014. "Semiparametric Conditional Quantile Models for Financial Returns and Realized Volatility," FinMaP-Working Papers 20, Collaborative EU Project FinMaP - Financial Distortions and Macroeconomic Performance: Expectations, Constraints and Interaction of Agents.
- Hua, Jian & Manzan, Sebastiano, 2013. "Forecasting the return distribution using high-frequency volatility measures," Journal of Banking & Finance, Elsevier, vol. 37(11), pages 4381-4403.
- Chowdhry, Bhagwan & Nanda, Vikram, 1998. "Leverage and Market Stability: The Role of Margin Rules and Price Limits," The Journal of Business, University of Chicago Press, vol. 71(2), pages 179-210, April.
- Luciano Gutierrez, 2013. "Speculative bubbles in agricultural commodity markets-super- †," European Review of Agricultural Economics, Oxford University Press and the European Agricultural and Applied Economics Publications Foundation, vol. 40(2), pages 217-238, March.
- Bates, David S., 2003. "Empirical option pricing: a retrospection," Journal of Econometrics, Elsevier, vol. 116(1-2), pages 387-404.
- Jin‐Chuan Duan, 1995. "The Garch Option Pricing Model," Mathematical Finance, Wiley Blackwell, vol. 5(1), pages 13-32, January.
- MacBeth, James D & Merville, Larry J, 1979. "An Empirical Examination of the Black-Scholes Call Option Pricing Model," Journal of Finance, American Finance Association, vol. 34(5), pages 1173-1186, December. Full references (including those not matched with items on IDEAS)
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Agricultural Finance; Risk And Uncertainty; Demand And Price Analysis;
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