M. Amiti and C. Freund, The Anatomy of China's Export Growth In: China's Growing Role in World Trade. NBER Chapters, National Bureau of Economic Research, pp.35-56, 2010.
DOI : 10.1596/1813-9450-4628

M. Amiti and J. Konings, Trade Liberalization, Intermediate Inputs, and Productivity: Evidence from Indonesia, American Economic Review, vol.97, issue.5, pp.1611-1638, 2007.
DOI : 10.1257/aer.97.5.1611

A. Antoniades, Heterogeneous Firms, Quality, and Trade, Journal of International Economics, vol.95, issue.2, 2008.
DOI : 10.1016/j.jinteco.2014.10.002

C. Arkolakis, A. Costinot, and A. Rodríguez-clare, New trade models, same old gains?, American Economic Review Forthcoming, 2011.

M. Asplund and R. Friberg, The Law of One Price in Scandinavian Duty-Free Stores, American Economic Review, vol.91, issue.4, pp.1072-1083, 2001.
DOI : 10.1257/aer.91.4.1072

R. Auer and A. M. Fischer, The effect of low-wage import competition on U.S. inflationary pressure, Journal of Monetary Economics, vol.57, issue.4, pp.491-503, 2010.
DOI : 10.1016/j.jmoneco.2010.02.007

R. A. Auer and P. U. Sauré, Spatial competition in quality, demand-induced innovation , and schumpeterian growth, 2011.

B. Y. Aw and M. J. Roberts, Measuring quality change in quota-constrained import markets: The Case of U.S. Footwear, Journal of International Economics, vol.21, issue.1-2, pp.45-60, 1986.
DOI : 10.1016/0022-1996(86)90004-8

B. Balassa, Tariff reductions and trade in manufacturers among the industrial countries, American Economic Review, vol.56, issue.3, pp.466-473, 1966.

R. Baldwin, V. Dinino, L. Fontagné, R. A. Santis, and D. Taglioni, Study on the impact of the euro on trade and foreign direct investment. European economy -economic papers, Directorate General Economic and Monetary Affairs, 2008.

R. Baldwin and J. Harrigan, Zeros, Quality, and Space: Trade Theory and Trade Evidence, American Economic Journal: Microeconomics, vol.3, issue.2, pp.60-88, 2011.
DOI : 10.1257/mic.3.2.60

URL : http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.255.6430

R. E. Baldwin, The euro's trade effect, Working Paper Series, vol.594, 2006.

P. Bastos and J. Silva, The quality of a firm's exports: Where you export to matters, Journal of International Economics, vol.82, issue.2, pp.99-111, 2010.
DOI : 10.1016/j.jinteco.2010.07.001

M. R. Baye, J. R. Gatti, P. Kattuman, and J. Morgan, DID THE EURO FOSTER ONLINE PRICE COMPETITION? EVIDENCE FROM AN INTERNATIONAL PRICE COMPARISON SITE, Economic Inquiry, vol.70, issue.4, pp.265-279, 2006.
DOI : 10.1093/ei/cbj015

P. Benigno and E. Faia, Globalization, pass-through and inflation dynamics, 2010.
DOI : 10.3386/w15842

P. R. Bergin, R. Glick, and J. Wu, The Micro-Macro Disconnect of Purchasing Power Parity, Review of Economics and Statistics, vol.80, issue.2, 2010.
DOI : 10.1111/j.1467-9957.2009.02097.x

E. Berman, J. Bound, and Z. Griliches, Changes in the Demand for Skilled Labor within U.S. Manufacturing: Evidence from the Annual Survey of Manufactures, The Quarterly Journal of Economics, vol.109, issue.2, pp.367-97, 1994.
DOI : 10.3386/w4255

E. Berman, J. Bound, and S. Machin, Implications Of Skill-Biased Technological Change: International Evidence, The Quarterly Journal of Economics, vol.113, issue.4, pp.1245-1279, 1998.

N. Berman, P. Martin, and T. Mayer, How do different exporters react to exchange rate changes? theory, empirics and aggregate implications. The Review of Economic Studies forthcoming, 2011.
URL : https://hal.archives-ouvertes.fr/hal-00973027

A. B. Bernard and J. B. Jensen, Exporters, skill upgrading, and the wage gap, Journal of International Economics, vol.42, issue.1-2, pp.3-31, 1997.
DOI : 10.1016/S0022-1996(96)01431-6

A. B. Bernard, J. B. Jensen, S. J. Redding, and P. K. Schott, Firms in International Trade, Journal of Economic Perspectives, vol.21, issue.3, pp.105-130, 2007.
DOI : 10.1257/jep.21.3.105

A. B. Bernard, J. B. Jensen, S. J. Redding, and P. K. Schott, Intra-firm Trade and Product Contractibility (long version) Nber working papers, National Bureau of Economic Research, 2010.
DOI : 10.3386/w15881

A. B. Bernard, J. B. Jensen, S. J. Redding, and P. K. Schott, The Empirics of Firm Heterogeneity and International Trade Working papers, 2011.

A. B. Bernard, J. B. Jensen, and P. K. Schott, Survival of the best fit: Exposure to low-wage countries and the (uneven) growth of U.S. manufacturing plants, Journal of International Economics, vol.68, issue.1, pp.219-237, 2006.
DOI : 10.1016/j.jinteco.2005.06.002

A. Berthou and L. Fontagné, The Euro and the Intensive and Extensive Margins of Trade: Evidence from French Firm Level Data, SSRN Electronic Journal, 2008.
DOI : 10.2139/ssrn.1194963

M. Bertrand, E. Duflo, and S. Mullainathan, How Much Should We Trust Differences-In-Differences Estimates?, The Quarterly Journal of Economics, vol.119, issue.1, pp.249-275, 2004.
DOI : 10.1162/003355304772839588

M. Bils and P. J. Klenow, Some Evidence on the Importance of Sticky Prices, Journal of Political Economy, vol.112, issue.5, pp.947-985, 2004.
DOI : 10.1086/422559

P. Biscourp and F. Kramarz, Employment, skill structure and international trade: Firm-level evidence for France, Journal of International Economics, vol.72, issue.1, pp.22-51, 2007.
DOI : 10.1016/j.jinteco.2006.07.005

J. Blaum, C. Lelarge, and M. Peters, Firm Heterogeneity and Import Behavior: Evidence from French Firms, pp.CREST-INSEE, 2010.

N. Bloom, M. Draca, and J. Van-reenen, Trade Induced Technical Change: The Impact of Chinese Imports on Innovation, 2009.

R. Boorstein and R. C. Feenstra, Quality Upgrading and its Welfare Cost in U.S. Steel Imports, 1969-74, National Bureau of Economic Research, 1987.
DOI : 10.3386/w2452

J. Brander and P. Krugman, A 'reciprocal dumping' model of international trade, Journal of International Economics, vol.15, pp.3-4, 1983.

J. A. Brander, Intra-industry trade in identical commodities, Journal of International Economics, vol.11, issue.1, pp.1-14, 1981.
DOI : 10.1016/0022-1996(81)90041-6

C. Broda and D. E. Weinstein, Globalization and the Gains From Variety, The Quarterly Journal of Economics, vol.121, issue.2, pp.541-585, 2006.
DOI : 10.1162/qjec.2006.121.2.541

A. Burstein, C. Kurz, and L. Tesar, Trade, production sharing, and the international transmission of business cycles, Journal of Monetary Economics, vol.55, issue.4, pp.775-795, 2008.
DOI : 10.1016/j.jmoneco.2008.03.004

N. Chen, J. Imbs, and A. Scott, The dynamics of trade and competition, Journal of International Economics, vol.77, issue.1, pp.50-62, 2009.
DOI : 10.1016/j.jinteco.2008.10.003

URL : https://hal.archives-ouvertes.fr/hal-00612547

G. Corsetti and L. Dedola, A macroeconomic model of international price discrimination, Journal of International Economics, vol.67, issue.1, pp.129-155, 2005.
DOI : 10.1016/j.jinteco.2004.09.009

M. Crozet, K. Head, T. Mayer, and . Forthcoming, Quality Sorting and Trade: Firm-level Evidence for French Wine, The Review of Economic Studies, vol.79, issue.2
DOI : 10.1093/restud/rdr030

URL : https://hal.archives-ouvertes.fr/hal-00973018

M. J. Crucini, C. I. Telmer, and M. Zachariadis, Understanding European Real Exchange Rates, American Economic Review, vol.95, issue.3, pp.724-738, 2005.
DOI : 10.1257/0002828054201332

E. Dhyne, L. J. Álvarez, H. L. Bihan, G. Veronese, D. Dias et al., Price Setting in the Euro Area: Some Stylized Facts from Individual Consumer Price Data, SSRN Electronic Journal, vol.524, 2005.
DOI : 10.2139/ssrn.1690504

J. Di-giovanni and A. A. Levchenko, Putting the Parts Together: Trade, Vertical Linkages, and Business Cycle Comovement, American Economic Journal: Macroeconomics, vol.2, issue.2, pp.95-124, 2010.
DOI : 10.1257/mac.2.2.95

F. Dicomite, J. Thisse, and H. Vandenbussche, Verti-zontal Differentiation in Monopolistic Competition, 2011.

A. Disdier and K. Head, The Puzzling Persistence of the Distance Effect on Bilateral Trade, Review of Economics and Statistics, vol.85, issue.2, pp.37-48, 2008.
DOI : 10.2307/146404

URL : https://hal.archives-ouvertes.fr/hal-01172854

J. Eaton and S. Kortum, Technology, Geography, and Trade, Econometrica, vol.70, issue.5, pp.1741-1779, 2002.
DOI : 10.1111/1468-0262.00352

J. Eaton, S. Kortum, and F. Kramarz, Dissecting Trade: Firms, Industries, and Export Destinations, American Economic Review, vol.94, issue.2, pp.150-154, 2004.
DOI : 10.1257/0002828041301560

J. Eaton, S. Kortum, and F. Kramarz, An Anatomy of International Trade: Evidence from French Firms, Econometrica forthcoming, 2011.
DOI : 10.3386/w14610

C. Engel, Real exchange rates and relative prices : An empirical investigation, Journal of Monetary Economics, vol.32, issue.1, pp.35-50, 1993.
DOI : 10.3386/w4231

C. Engel and J. H. Rogers, How Wide Is the Border?, American Economic Review, vol.86, issue.5, pp.1112-1137, 1996.
DOI : 10.3386/w4829

C. Engel and J. H. Rogers, European product market integration after the euro, Economic Policy, vol.19, issue.39, pp.347-384, 2004.
DOI : 10.1111/j.1468-0327.2004.00126.x

R. Feenstra, New Product Varieties and the Measurement of International Prices, The American Economic Review, vol.84, issue.1, pp.157-177, 1994.

R. C. Feenstra and S. Wei, China's Growing Role in World Trade. No. 07-1 in NBER Books, National Bureau of Economic Research, 2010.

D. Fitzgerald and S. Haller, Pricing-to-Market: Evidence From Plant-Level Prices, The Review of Economic Studies, vol.81, issue.2, 2010.
DOI : 10.1093/restud/rdt045

L. Fontagné, T. Mayer, and G. Ottaviano, Of markets, products and prices: The effects of the euro on European firms, Intereconomics, vol.44, issue.3, pp.149-158, 2009.
DOI : 10.1007/s10272-009-0289-8

L. Fontagné, G. Gaulier, and S. Zignago, Specialization across varieties and North-South competition, Economic Policy, vol.23, issue.53, pp.51-91, 2008.
DOI : 10.1111/j.1468-0327.2007.00193.x

L. Foster, J. Haltiwanger, and C. Syverson, Reallocation, Firm Turnover, and Efficiency: Selection on Productivity or Profitability?, American Economic Review, vol.98, issue.1, pp.394-425, 2008.
DOI : 10.1257/aer.98.1.394

D. Fougere, E. Gautier, and H. L. Bihan, Restaurant Prices and the Minimum Wage, SSRN Electronic Journal, vol.42, issue.7, pp.1199-1234, 2010.
DOI : 10.2139/ssrn.1679676

R. Friberg, Common Currency, Common Market?, ), pp.650-661, 2003.
DOI : 10.1162/154247603322391288

URL : http://hdl.handle.net/10419/108048

R. Friberg and T. Y. Matha, Does a common currency lead to (more) price equalization? The role of psychological pricing points, Economics Letters, vol.84, issue.2, pp.281-287, 2004.
DOI : 10.1016/j.econlet.2004.01.013

X. Gabaix, The granular origins of aggregate fluctuations, Econometrica, vol.79, issue.3, pp.733-772, 2011.

J. J. Gabszewicz and J. F. Thisse, Price competition, quality and income disparities, Journal of Economic Theory, vol.20, issue.3, pp.340-359, 1979.
DOI : 10.1016/0022-0531(79)90041-3

G. Gaulier and S. Zignago, A world database of international trade analysis at the product level. Cepii working papers, 2008.

E. Gautier, The behaviour of producer prices: evidence from French PPI micro data, Empirical Economics, vol.28, issue.1, pp.301-332, 2008.
DOI : 10.1007/s00181-007-0160-3

S. Gil-pareja and S. Sosvilla-rivero, Price convergence in the European car market, Applied Economics, vol.86, issue.2, pp.241-250, 2008.
DOI : 10.1080/1350485042000187453

URL : https://hal.archives-ouvertes.fr/hal-00582037

L. S. Goldberg and J. M. Campa, The Sensitivity of the CPI to Exchange Rates: Distribution Margins, Imported Inputs, and Trade Exposure, Review of Economics and Statistics, vol.81, issue.4, pp.392-407, 2010.
DOI : 10.1016/S0022-1996(98)00009-9

P. K. Goldberg and R. Hellerstein, A structural approach to identifying the sources of local-currency price stability. Nber working papers, National Bureau of Economic Research, 2007.

P. K. Goldberg, A. K. Khandelwal, N. Pavcnik, and P. Topalova, Imported Intermediate Inputs and Domestic Product Growth: Evidence from India, The Quarterly Journal of Economics, vol.125, issue.4, pp.1727-1767, 2010.
DOI : 10.1162/qjec.2010.125.4.1727

URL : http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.147.7611

P. K. Goldberg and M. M. Knetter, Goods Prices and Exchange Rates: What Have We Learned, Journal of Economic Literature, vol.35, issue.3, pp.1243-1272, 1997.
DOI : 10.3386/w5862

P. K. Goldberg and F. Verboven, The Evolution of Price Dispersion in the European Car Market, The Review of Economic Studies, vol.68, issue.4, pp.811-859, 2001.
DOI : 10.1111/1467-937X.00191

G. Gopinath and B. Neiman, Trade adjustment and productivity in large crises. Nber working papers, National Bureau of Economic Research, 2011.

H. Gorg, L. Halpern, B. Muraközy, and . Feb, Why do within firm-product export prices differ across markets? Kiel Working Papers 1596, 2010.

M. L. Greenhut, H. Ohta, and J. Sailors, Reverse Dumping: A Form of Spatial Price Discrimination, The Journal of Industrial Economics, vol.34, issue.2, pp.167-81, 1985.
DOI : 10.2307/2098680

H. G. Grubel and P. J. Lloyd, The Empirical Measurement of Intra-Industry Trade, Economic Record, vol.5, issue.4, pp.494-517, 1971.
DOI : 10.2307/2226976

J. C. Hallak, Product quality and the direction of trade, Journal of International Economics, vol.68, issue.1, pp.238-265, 2006.
DOI : 10.1016/j.jinteco.2005.04.001

J. C. Hallak, P. K. Schott, and . Forthcoming, Estimating Cross-Country Differences in Product Quality, The Quarterly Journal Of Economics

J. C. Hallak and J. Sivadasan, Firms' exporting behavior under quality constraints . Working Paper 14928, National Bureau of Economic Research, 2009.
DOI : 10.3386/w14928

URL : http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.555.7607

J. Harrigan, Airplanes and comparative advantage. Working Paper 11688, National Bureau of Economic Research, 2005.
DOI : 10.1016/j.jinteco.2010.07.002

J. Harrigan and G. Barrows, Testing the Theory of Trade Policy: Evidence from the Abrupt End of the Multifiber Arrangement, Review of Economics and Statistics, vol.84, issue.1, pp.282-294, 2009.
DOI : 10.1257/0002828042002633

J. Harrigan and H. Deng, China's local comparative advantage. Nber working papers, National Bureau of Economic Research, 2008.

R. Hausmann, J. Hwang, and D. Rodrik, What you export matters, Journal of Economic Growth, vol.106, issue.1, pp.1-25, 2007.
DOI : 10.1007/s10887-006-9009-4

M. Helbe and T. Okubo, Heterogeneous Quality Firms and Trade Costs, 2008.

R. Hellerstein and S. B. Villas-boas, Outsourcing and pass-through, Journal of International Economics, vol.81, issue.2, pp.170-183, 2010.
DOI : 10.1016/j.jinteco.2010.03.004

B. Hobijn, F. Ravenna, and A. Tambalotti, Menu Costs at Work: Restaurant Prices and the Introduction of the Euro*, Quarterly Journal of Economics, vol.121, issue.3, pp.1103-1131, 2006.
DOI : 10.1162/qjec.121.3.1103

E. M. Hoover and J. , Spatial Price Discrimination, The Review of Economic Studies, vol.4, issue.3, pp.182-191, 1937.
DOI : 10.2307/2967453

H. A. Hopenhayn, Entry, Exit, and firm Dynamics in Long Run Equilibrium, Econometrica, vol.60, issue.5, pp.1127-50, 1992.
DOI : 10.2307/2951541

D. Hummels, J. Ishii, and K. Yi, The nature and growth of vertical specialization in world trade, Journal of International Economics, vol.54, issue.1, pp.75-96, 2001.
DOI : 10.1016/S0022-1996(00)00093-3

D. Hummels and P. J. Klenow, The Variety and Quality of a Nation's Exports, American Economic Review, vol.95, issue.3, pp.704-723, 2005.
DOI : 10.1257/0002828054201396

D. Hummels and V. Lugovskyy, Are Matched Partner Trade Statistics a Usable Measure of Transportation Costs?*, Review of International Economics, vol.40, issue.1, pp.69-86, 2006.
DOI : 10.1093/wber/15.3.451

D. Hummels and V. Lugovskyy, International Pricing in a Generalized Model of Ideal Variety, Journal of Money, Credit and Banking, vol.112, issue.s1, pp.3-33, 2009.
DOI : 10.1111/j.1538-4616.2008.00197.x

D. Hummels and A. Skiba, Shipping the Good Apples Out? An Empirical Confirmation of the Alchian???Allen Conjecture, Journal of Political Economy, vol.112, issue.6, pp.1384-1402, 2004.
DOI : 10.1086/422562

A. Irarrazabal, A. Moxnes, L. D. Opromolla, and . Feb, The tip of the iceberg: Modeling trade costs and implications for intra-industry reallocation, CEPR Discussion Papers 7685, C.E.P.R. Discussion Papers, 2010.

R. Johnson, Trade and prices with heterogeneous firms, Journal of International Economics, vol.86, issue.1, 2008.
DOI : 10.1016/j.jinteco.2011.09.004

A. Khandelwal, The Long and Short (of) Quality Ladders, Review of Economic Studies, vol.77, issue.4, pp.1450-1476, 2010.
DOI : 10.1111/j.1467-937X.2010.00602.x

A. K. Khandelwal, P. K. Schott, and S. Wei, Trade Liberalization and Embedded Institutional Reform: Evidence from Chinese Exporters, 2011.
DOI : 10.3386/w17524

M. M. Knetter and M. J. Slaughter, Measuring Market-Product Integration, Working Paper National Bureau of Economic Research, vol.6969, 1999.
DOI : 10.7208/chicago/9780226060859.003.0002

I. Kravis and R. Lipsey, International Trade Prices and Price Proxies The Role of the Computer in Economic and Social Research in Latin America, pp.253-66, 1974.

P. Krugman, Scale Economies, Product Differentiation, and the Pattern of Trade, American Economic Review, vol.70, issue.5, pp.950-59, 1980.

M. Lutz, Price Convergence under EMU? First Estimates, Royal Economic Society Annual Conference, 2003.

S. Machin and J. V. Reenen, Technology and Changes in Skill Structure: Evidence from Seven OECD Countries, The Quarterly Journal of Economics, vol.113, issue.4, pp.1215-1244, 1998.
DOI : 10.1162/003355398555883

K. Manova, Z. Zhang, and . Forthcoming, Export Prices across Firms and Destinations, The Quarterly Journal of Economics

T. Mayer, Market potential and development. CEPR Discussion Papers 6798, C.E.P.R. Discussion Papers, 2008.
URL : https://hal.archives-ouvertes.fr/hal-01066164

T. Mayer and G. Ottaviano, The happy few: new facts on the internationalisation of European firms, 2007.

T. Mayer and S. Zignago, Geodist: the CEPII's distances and geographical database. MPRA Working Paper 31243, 2006.

J. Mccarthy, Pass-Through of Exchange Rates and Import Prices to Domestic Inflation in Some Industrialized Economies, Eastern Economic Journal, vol.33, issue.4, pp.511-537, 2007.
DOI : 10.1057/eej.2007.38

I. Méjean and C. Schwellnus, Price convergence in the European Union: Within firms or composition of firms?, Journal of International Economics, vol.78, issue.1, pp.1-10, 2009.
DOI : 10.1016/j.jinteco.2009.02.008

M. J. Melitz, The Impact of Trade on Intra-Industry Reallocations and Aggregate Industry Productivity, Econometrica, vol.71, issue.6, pp.1695-1725, 2003.
DOI : 10.1111/1468-0262.00467

M. J. Melitz and G. I. Ottaviano, Market Size, Trade, and Productivity, Review of Economic Studies, vol.75, issue.1, pp.295-316, 2008.
DOI : 10.1111/j.1467-937X.2007.00463.x

G. Mion and L. Zhu, Import competition from and outsourcing to China: a curse or blessing for firms? CEPR Discussion Papers 8188, C.E.P.R, 2011.

E. Nakamura and D. Zerom, Accounting for Incomplete Pass-Through, Review of Economic Studies, vol.77, issue.3, pp.1192-1230, 2010.
DOI : 10.1111/j.1467-937X.2009.589.x

B. Neiman, Stickiness, synchronization, and passthrough in intrafirm trade prices, Journal of Monetary Economics, vol.57, issue.3, pp.295-308, 2010.
DOI : 10.1016/j.jmoneco.2010.02.002

G. Ottaviano, T. Tabuchi, and J. Thisse, Agglomeration and Trade Revisited*, International Economic Review, vol.21, issue.2, pp.409-436, 2002.
DOI : 10.1111/1468-2354.t01-1-00021

URL : http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.21.7376

A. K. Rose, One money, one market: the effect of common currencies on trade, Economic Policy, vol.15, issue.30, pp.7-46, 2000.

J. D. Sachs and H. J. Shatz, Trade and jobs in manufacturing, Brookings Papers on Economic Activity, vol.25, issue.1, pp.1-84, 1994.

K. Sato, The Ideal Log-Change Index Number, The Review of Economics and Statistics, vol.58, issue.2, pp.223-251, 1976.
DOI : 10.2307/1924029

R. Schoenle, International Menu Costs and Price Dynamics, Review of International Economics, vol.86, issue.3, 2010.
DOI : 10.1111/roie.12275

P. K. Schott, Across-Product Versus Within-Product Specialization in International Trade, The Quarterly Journal of Economics, vol.119, issue.2, pp.646-677, 2004.
DOI : 10.1162/0033553041382201

P. K. Schott, The relative sophistication of Chinese exports, Economic Policy, vol.23, issue.53, pp.5-49, 2008.
DOI : 10.1111/j.1468-0327.2007.00195.x

M. Silver, Do unit value Export, Import, and Terms of Trade Indices Represent or Misrepresent Price Indices? IMF Working Paper 07, 2007.

V. Strauss-kahn, The Role of Globalization in the Within-Industry Shift Away from Unskilled Workers in France, Challenges to Globalization, 2004.

A. M. Taylor and M. P. Taylor, The Purchasing Power Parity Debate, Journal of Economic Perspectives, vol.18, issue.4, pp.135-158, 2004.
DOI : 10.1257/0895330042632744

J. Tirole, The Theory of Industrial Organization, eleventh printing, Edition, vol.1, 1988.

Y. Vartia, Ideal Log-Change Index Numbers, Scandinavian Journal of Statistics, vol.3, issue.3, pp.121-147, 1976.

J. M. Wooldridge, Cluster-Sample Methods in Applied Econometrics, American Economic Review, vol.93, issue.2, 2005.
DOI : 10.1257/000282803321946930

T. Currency, 155 5 Frequency and monthly duration of price changes, p.168