Phát triển tài chính và tăng trưởng kinh tế

BỘ GIÁO DỤC VÀ ĐÀO TẠO TRƯỜNG ĐẠI HỌC KINH TẾ TP HỒ CHÍ MINH Phạm Dương Phương Thảo PHÁT TRIỂN TÀI CHÍNH VÀ TĂNG TRƯỞNG KINH TẾ LUẬN ÁN TIẾN SĨ KINH TẾ Tp Hồ Chí Minh - Năm 2019 BỘ GIÁO DỤC VÀ ĐÀO TẠO TRƯỜNG ĐẠI HỌC KINH TẾ TP HỒ CHÍ MINH Phạm Dương Phương Thảo PHÁT TRIỂN TÀI CHÍNH VÀ TĂNG TRƯỞNG KINH TẾ Chuyên ngành: Tài – Ngân hàng Mã số: 9340201 LUẬN ÁN TIẾN SĨ KINH TẾ NGƯỜI HƯỚNG DẪN KHOA HỌC: PGS.TS PHAN THỊ BÍCH NGUYỆT Tp Hồ Chí Minh – Năm 2019 Trang i LỜI CAM ĐOAN Tôi xin cam đoan luận án tiến sĩ với đề tài “Phát triển tài Tăng trưởng kinh tế” cơng trình nghiên cứu độc lập Các thông tin, số liệu luận án trung thực, có nguồn gốc trích dẫn rõ ràng, cụ thể chưa công bố cơng trình nghiên cứu khác TP.HCM, ngày 01 tháng 12 năm 2019 Nghiên cứu sinh Phạm Dương Phương Thảo Trang ii MỤC LỤC Contents LỜI CAM ĐOAN i MỤC LỤC ii DANH MỤC TỪ VIẾT TẮT vi DANH MỤC BẢNG .vii DANH MỤC HÌNH ix TRANG THÔNG TIN NHỮNG ĐIỂM MỚI CỦA LUẬN ÁN x CONTRIBUTION OF THE THESIS xii TÓM TẮT xiii ABSTRACT xiv CHƯƠNG MỞ ĐẦU 1.1 Bối cảnh nghiên cứu luận án 1.2 Khoảng trống nghiên cứu 1.3 Vấn đề nghiên cứu mục tiêu nghiên cứu 1.4 Đối tượng phạm vi nghiên cứu 1.5 Phương pháp nghiên cứu 1.6 Tóm tắt kết nghiên cứu 11 1.7 Những đóng góp luận án 12 1.8 Kết cấu luận án 13 CHƯƠNG 2TỔNG QUAN LÝ THUYẾT VÀ NGHIÊN CỨU TRƯỚC ĐÂY 15 2.1 Tăng trưởng kinh tế 16 2.1.1 Phân biệt Tăng trưởng kinh tế Phát triển kinh tế 16 Trang iii 2.1.2 Hàm sản xuất 16 2.1.3 Đo lường tăng trưởng kinh tế 17 2.2 Phát triển tài 18 2.2.1 Hệ thống tài 18 2.2.2 Sự phát triển tài 20 2.2.3 Đo lường phát triển tài 22 2.2.3.1 Tỷ số tín dụng cho khu vực tư nhân GDP 22 2.2.3.2 Tỷ số tín dụng nội địa GDP 23 2.2.3.3 Tỷ số cung tiền GDP 23 2.2.3.4 Các chỉ tiêu đo lường thị trường tài so với GDP 25 2.2.3.5 Các phương pháp đo lường khác 26 2.3 Vai trò phát triển tài lý thuyết tăng trưởng kinh tế 30 2.4 Bằng chứng thực nghiệm tác động Phát triển tài đến Tăng trưởng kinh tế 35 2.4.1 Tác động tích cực Phát triển tài đến tăng trưởng kinh tế 36 2.4.2 Tác động phi tuyến Phát triển tài lên Tăng trưởng kinh tế 43 Kết luận chương 54 CHƯƠNG PHƯƠNG PHÁP NGHIÊN CỨU 55 3.1 Câu hỏi nghiên cứu giả thuyết nghiên cứu 55 3.2 Dữ liệu nghiên cứu 58 3.3 Mơ hình nghiên cứu 60 3.4 Các biến số mơ hình 64 3.4.1 Biến phụ thuộc (Tăng trưởng kinh tế - GROWTH) 64 3.4.2 Biến độc lập (Phát triển tài – FD) 65 Trang iv 3.4.3 Các biến kiểm soát 66 3.5 Phương pháp ước lượng 72 3.5.1 Phương pháp hồi quy ngưỡng dành cho liệu bảng 74 3.5.2 Phương pháp hồi quy GMM 79 Kết luận chương 81 CHƯƠNG KẾT QUẢ NGHIÊN CỨU 82 4.1 Thống kê mô tả 82 4.2 Phân tích tác động phi tuyến phát triển tài đến tăng trưởng kinh tế liệu ngân hàng 87 4.2.1 Kết hồi quy ngưỡng 87 4.2.1.1 Tín dụng cho khu vực tư nhân 87 4.2.1.2 Tín dụng nước 94 4.2.1.3 Nợ khoản /GDP 96 4.2.2 Kết ước lượng system-GMM 101 4.3 Phân tích tác động phi tuyến phát triển tài đến tăng trưởng kinh tế liệu TTCK 105 4.3.1 Kết hồi quy ngưỡng 105 4.3.1.1 Quy mô vốn hóa thị trường/GDP 105 4.3.1.2 Vòng quay TTCK 108 4.3.1.3 Quy mô giao dịch TTCK/GDP 109 4.3.2 Kết ước lượng GMM 113 4.4 Phân tích mẫu phụ 115 4.4.1 Thống kê mô tả 115 4.4.2 Phân tích mẫu phụ High income 117 Trang v 4.4.3 Phân tích mẫu phụ Middle income 119 Kết luận chương 123 CHƯƠNG KHUYẾN NGHỊ CHÍNH SÁCH PHÁT TRIỂN TÀI CHÍNH ĐỂ TĂNG TRƯỞNG KINH TẾ TẠI CÁC NƯỚC CHÂU Á 125 5.1 Cơ cấu phát triển cách thức quản lý hệ thống tài cần linh hoạt, tăng khả cạnh tranh 126 5.2 Minh bạch thơng tin hoạt động hệ thống tài 128 5.3 Đảm bảo an toàn cho hệ thống tài 129 5.4 Chính sách tiền tệ linh hoạt 130 5.5 Phát triển khu vực tài mực 131 5.6 Hiện đại hóa hệ thống tài 132 5.7 Nâng cao vai trò chủ thể tham gia hệ thống tài 133 5.8 Các ý kiến đề xuất khác 134 5.9 Hạn chế đề tài hướng nghiên cứu tương lai 136 DANH MỤC CÁC CƠNG TRÌNH ĐÃ CƠNG BỐ 138 TÀI LIỆU THAM KHẢO 139 PHỤ LỤC 151 Trang vi DANH MỤC TỪ VIẾT TẮT ADB: Asian Development Bank ARDL: Auto Regressive Distributed Lag GDP: Gross Domestic Product GNP: Gross National Product GFDD: Global Financial Development Database GMM: Generalized Method of Moments IMF: International Monetary Fund TTCK: Thị trường chứng khốn UNDP: Chương trình Phát triển Liên Hiệp Quốc UAE: Các Tiểu vương quốc Ả Rập Thống Nhất WDI: World Development Indicators WGI: World Governance Indicators 2SLS: 2-Stage Least Squares Trang vii DANH MỤC BẢNG Bảng 2.1 Tóm lược lý thuyết tăng trưởng kinh tế 29 Bảng 3.1 Phân loại nước mẫu theo thu nhập 60 Bảng 3.2 Các biến số mơ hình nghiên cứu 72 Bảng 4.1 Thống kê mơ tả tồn mẫu 82 Bảng 4.2 Thống kê chỉ tiêu Phát triển tài tồn mẫu 84 Bảng 4.3 Ma trận tương quan biến mơ hình nghiên cứu 86 Bảng 4.4 Kết hồi quy ngưỡng với FD đo lường Tín dụng cho khu vực tư nhân/GDP 88 Bảng 4.5 Kiểm định tồn ngưỡng FD =Tín dụng cho khu vực tư nhân/GDP 89 Bảng 4.6 Kiểm định tồn ngưỡng FD =Tín dụng nước /GDP 94 Bảng 4.7 Kết hồi quy ngưỡng với FD = Tín dụng nước /GDP 95 Bảng 4.8 Kiểm định tồn ngưỡng FD = Nợ khoản /GDP 96 Bảng 4.9 Kết hồi quy ngưỡng với FD = Nợ khoản /GDP 97 Bảng 4.10 Tóm tắt kết hồi quy ngưỡng (bank-based) 99 Bảng 4.11 Kết hồi quy ngưỡng với nguồn vốn người đo HDI 100 Bảng 4.12 Giá trị ngưỡng Phát triển tài (bank-based) 101 Bảng 4.13 Kết system-GMM (bank-based) 103 104 Bảng 4.14 Kiểm định Ho: ( + = 0) Bảng 4.15 Kiểm định giá trị ngưỡng FD= Quy mơ vốn hóa TTCK/GDP .105 Bảng 4.16 Kết hồi quy ngưỡng FD = Quy mơ vốn hóa TTCK/GDP 106 Bảng 4.17 Kết hồi quy ngưỡng FD = Vòng quay TTCK 108 Bảng 4.18 Kiểm định giá trị ngưỡng FD = Vòng quay TTCK 109 Bảng 4.19 Kiểm định giá trị ngưỡng FD = Quy mô giao dịch TTCK / GDP 109 Trang viii Bảng 4.20 Kết hồi quy ngưỡng FD = Quy mô giao dịch TTCK/GDP 110 Bảng 4.21 Tóm tắt kết hồi quy ngưỡng với FD đo liệu TTCK 111 Bảng 4.22 Tóm tắt giá trị ngưỡng Phát triển tài (market-based) 112 Bảng 4.23 Kết GMM liệu TTCK 113 Bảng 4.24 Thống kê mô tả mẫu High income 115 Bảng 4.25 Thống kê mô tả mẫu Middle income 116 Bảng 4.26 Kết hồi quy ngưỡng mẫu phụ High income 117 Bảng 4.27 Kiểm định tồn ngưỡng mẫu phụ High income 119 Bảng 4.28 Kết hồi quy mẫu phụ Middle income 120 Bảng 4.29 Kiểm định tồn ngưỡng mẫu phụ Middle income .121 Bảng 4.30 Ngưỡng Phát triển tài mẫu phụ tồn mẫu .122 11 CHAPTER RESEARCH METHODOLOGY 3.1 Research method Panel data is used to analyze in this thesis for its advantage that combines both dimensions of countries and time Panel Threshold Regression model for panel data by Hansen (1999) is used This model is then developed by Wang (2015) in Stata software with the feature of Fixed Effect This method requires data to be completely balanced panel Based on King and Levine (1993 a,b) combining with threshold function in Law and Singh (2014), the threshold regression model in this thesis takes the following form: + = ( + > )+ + ( ≤ )+ ( ≤ ) + i = 1,…,N is country t = 1,…,T is time µi is the country-specific fixed effect is the time effect The level of financial development (FD variable) is the threshold variable used to split the sample into two regimes FD variable plays the role as explanatory variable λ is the unknown threshold parameter 12 I(.) is the indicator function, which takes the value if the argument in parenthesis is valid, and otherwise This type of modelling strategy allows the role of finance to differ, depending on whether FD is below or above some unknown level of λ Effects of FD on the depending variable GROWTH is divided into different regimes, recognized by different β1 and β2 As a result, it is possible to capture the changing effect of the FD explanatory variable when passing the threshold value, and at the same time determine the value of the threshold For consistency of results, in this thesis, the author in turn adds other explanatory variables to the regression model Other methods to test the consistency of results are also carried out including: Use different proxies: the key explanatory variable in the model is FD – for the financial development – will be measured with different proxies: Private credit to GDP; Domestic credit to GDP; Liquid liabilities (M3) to GDP (Law Singh, 2014); Stock market capitalization to GDP; Stock traded, total value (% of GDP); Stock market turnover ratio (%) (Cihak cộng sự, 2012) Analyze in sub-sample: Split the research sample into subsamples based on criteria of classifying country by income GNI per capita, World Bank 2017 Use another econometric method: Dummy variable is used to divide the research sample into regimes based on the threshold value 13 found with Panel Threshold Regression This dummy variable takes the value if FD is over threshold, and otherwise Interactive variable formed between the dummy and FD is added into the model System – GMM method by Arellano and Bond (1991) is used to analyze effect of finance on growth before and after the threshold The application of another economic method GMM is to solve potential problems of the model such as endogeneity, heteroskedasticity, autocorrelation Furthermore, using GMM method as an alternative for analysis of the same research problem is also the way to consider whether the research results are consistent or not 3.2 Data The object of this study is economic growth and financial system development in 33 countries Data of countries in the sample are assessed on both aspects: bank based and stock market based However, when analyzing the level of financial development in terms of financial markets, the sample must be excluded Brunei, Maldives, Cambodia, Myanmar, and Taijikistan because there is no stock market in these countries; and excluded Armenia, Bangladesh, Kuwait, Kyrgyz Republic, Nepal, Mongolia because of no data in 2013-2016 That’s why analysis with stock market based data has only 22 countries in 2004-2016 14 Table 3.1 Variables in the research models Factor Variable Economic growth GROWTH GDP growth (annual %) % WDI privatecre Private credit to GDP % WDI domescre Domestic credit to GDP % WDI liq Liquid liabilities (M3) to GDP % GFDD smcapliz Stock market capitalization to GDP % GFDD smturnover Stock market turnover ratio (%) % GFDD smtrade Stock traded, total value (% of GDP) % GFDD Population pop Population growth (annual) % WDI Income income GDP per capita Investment invest Gross capital formation (% of GDP) % WDI Trade tradeop Trade openness to GDP % WDI Inflation infla Inflation rate based on CPI % WDI Institution inst Average score of index WGI Human capital mys Average year of schooling UNDP hci Human Capital Index development Source WDI year Financial Meaning UNDP Source: the author’s 15 CHAPTER 4: RESEARCH RESULTS The sample includes 33 Asian economies in the period of 20042016 to make a balanced panel Descriptive statistics in Table 4.1 showing that Asian economies in the sample have average economic growth about 5,37% with maximum of 26,17% Compared with developed economies in Europe and America, these growth rates are rather high thank for the fact that there are many emerging economies in the sample such as China, India, Japan, Indonesia, South Korea, Turkey, Iran, Saudi Arab, Russia, Singapore, and Thailand which have a rapid growth rate in the modern period However, the global financial crisis 2008 is in the research period, so it is inevitable that some markets could not maintain the high growth rate as before, and even decrease such as -14,15% (Armenia in 2009) The average GDP per capita of countries in the sample is 14 055,7 USD/year Table 4.1 Descriptive Statistics N Mean SD Min Max growth 429 5,377195 4,277762 -14,15 26,1702 pop 429 2,033399 2,440679 -0,8638 16,3316 income 429 14055,7 17567,18 491,6975 72670,96 invest 429 27,51565 7,944809 10,3775 58,1507 tradeop 429 94,68592 66,81454 0,1674 441,6038 16 infla 429 5,938118 5,431072 -4,8633 39,2664 goexp 429 13,68105 5,038939 3,4603 30,0035 inst 429 -0,2190224 0,6902128 -1,7516 1,5922 mys 429 8,415385 2,579076 2,7 12,8 hci 429 2,55965 0,597483 3,71 privatecre 429 58,65262 39,22993 3,1211 173,537 domescre 429 71,82900 59,13059 -10,1518 345,7219 liquid 429 65,41786 42,66564 6,7058 217,702 Source: the author’s The results of Panel Threshold Regression are shown briefly in Table 4.2 confirm that in Asian countries, financial development is not only positive, it can also have a negative impact on economic growth in different value areas of the measure of financial development In another words, the relationship between financial development and economic growth is nonlinear; there appears a threshold value of financial development that, above this threshold, the impact caused by financial development changes compared to the previous one Table 4.2 Threshold value of Financial Development (bankbased) Financial development threshold Min Max Private credit to GDP Domestic credit to GDP 8,9762 8,8641 8,4427 8,1817 9,3103 9,2651 M3/GDP 18,4802 17,9976 19,6984 Source: the author’s 17 Empirical results with the whole sample are similar with the ones in sub-samples, confirming that threshold value: Private credit should be 8,9762% of GDP; Domestic credit is 8,8641% of GDP; Liquid liabilities (or broad money M3) should be 18,0957% of GDP In the aspect of stock market, threshold value are as following: Stock market capitalization is 81,8477% of GDP; Stock market turnover ratio should be 27,3429%, stock market, traded value should be 51,2688% of GDP All results from bank-based data are significant, showing that in the regime under the threshold value, financial development enhances economic growth but in the over-regime, it shows negative effect However, with stock market based data, financial development has positive correlation in the under-regime but in the over-regime, it still has positive effect with smaller level This implies that financial development still enhances economic growth when finance is over the threshold but the level is decreased Table 4.3 shows these findings 18 Table 4.3 Threshold Regression with stock market based data FD= Stock market FD = Stock capitalization market turnover Threshold 81,8477 (estimator 95%) FD= Stock traded (72,4982; 27,3429 51,2688 (26,1388; (44,6318; 81,9182) 27,8660) Under threshold Over threshold 52,8341) 0,0450*** 0,0707*** 0,0438*** (0,000) (0,000) (0,000) 0,0289*** 0,0081 0,0034 (0,000) (0,230) (0,415) Source: the author’s This result implies that developing and developing countries in Asia can still pursue economic growth targets by developing financial sector more to promote its effects on the economy.However, high level of financial development does not always beneficial for national economic growth Nowadays, an optiomal level of financial development which fosters sustainable growth should be taken into consideration for those countries 19 CHAPTER 5: SOLUTIONS AND RECOMMENDATIONS FOR FINANCIAL DEVELOPMENT TO ECONOMIC GROWTH IN ASIAN COUNTRIES The key issue here for policy is not extended operations of banking sector or stock market, but it is emphasized that solutions should focus on exploiting the effectiveness and positive role of financial development In this way, pursuing goals of Asian countries - which is sustainable economic growth, reducing the gap with developed countries in the world - could be achieved in long term Based on the results of this research, some solutions and recommendation are suggested in order to develop financial system properly, aiming to economic growth sustainably in long term as following: 5.1 Structure of financial system development and managing methods should be flexible and increase competitiveness The positive contribution financial system can make to economic growth process depends on its design and operation Therefore, the choice of structure to develop financial system should ensure the principle of flexibility and respect for the market Asian financial markets have unequal development, which does not create a real competitive environment for capital Low capital account liberalization, simple products, lack of popular derivative 20 products also reduce the efficiency and make the market not attractive to foreign investors The results of this thesis show that threshold values of financial development in Asian economies are not high What these countries need to in their financial system development strategy is not expansion in size or quantity, but must focus on in-depth financial development, increased efficiency and adding value The results also imply that there is a need to improve the effectiveness of monetary policy and the management of banking system operations in these countries Solutions are not discrete, but in an overall process of improving quantity, quality, and efficiency of services of financial intermediaries; relating to the operation and interaction of many different organizations and individuals in the financial market 5.2 Information transparency in the operation of the financial system Financial markets perform well, which is reflected in their efficiency and liquidity (Dorruci cộng sự, 2009) Meanwhile, the problem which exists for a long time, is the barrier in financial market of developing Asian countries is the information asymmetry This always happens in the process of mobilizing and using capital Therefore, ensuring the transparency of information in the operation of financial system should be a top goal in developing operational strategies, building a full legal frame and regulations for the operation of banking system and other intermediary financial institutions, for trading on capital markets and stock markets 21 5.3 Security for financial system In order to develop financial sector strongly and sustainably, for promoting economic growth, it is necessary to carry out financial safety supervision in the monetary market, banking system, stock market, and other financial markets such as insurance market The most important thing is ensuring the ratio of available capital, periodically report to the market management agency For the operation of monetary market and banking sector: apply international standards such as Basel II, CAMELS to ensure safety in operation 5.4 Flexible monetary policy It is necessary to maintain flexible and adaptive monetary policy, strengthen fiscal situation and moderate credit growth to strengthen macroeconomic policy framework and enhance resilience to economic shocks For financial development, flexible monetary policies and sensitive solutions based on actual movements of the market are essential However, this development had better ensure optimization at an appropriate level to promote economic growth 5.5 Suitable level of financial development Nowadays, World Bank encourages UFA (Universal Financial Access) that is more accessing of people to the financial system is an important factor to help reduce poverty and improve economic growth So, up to 2020 UFA should be done globally Many countries including Vietnam have agreed to participate in this agreement Nevertherless, developing Asian countries shouls realize 22 that financial development is a process of improving both the quantity, quality and efficiency of the financial system in relation to the operation and interaction of various organizations and individuals in the market They should develop the financial sector both in width and depth at a proper level Excessive financial development at all costs, the positive role and promote economic growth of the financial system will be eliminated 5.6 Modernization of financial system Strong, safe, efficient, and broadly developed infrastructure for finance will contribute to the efficiency of trading account services, expanding network, and diversifying payment products and services to meet the diversity of people needs 5.7 Increase role of entities participating in the financial system From experience of Singapore, countries whose financial system still low developed can learn how to make policy for financial development: It’s important to focus on develop for all entities in the market rather than creating specific incentives for government-managed financial institutions This leads to fair environment, encouraging fair competition in the financial market, making right motivation for financial system to develop 5.8 Other suggestions The thesis also found conclusions regarding control variables Based on the results of this study to propose the following additional solutions: 23  Reduce government expenditure to make less budget deficit and ensure financial security Improve the efficiency of government expenditures  Infrastructure investment should be focused effectively, minimizing investment in wrong objectives Encourage PublicPrivate Partnership  Strengthening the role of supervision and consultancy of socio-political organizations; Build-up, supplement, amend the relevant provisions of the current laws  Promote structural reforms, including business and banking sector reforms; implement policies to promote trade liberalization  Continue to improve the legal framework, mechanisms and policies for the operation of the financial system, improve the institutional environment, attract human capital - i.e high-quality workers  For gainning growth in long run in developing Asian countries like Vietnam, there should be institutional reform in a comprehensive manner, developing legal regulations to suit the reality 5.9 Limitation and future research This study also cannot avoid some limitation: not many countries with enough data to be collected, so the sample size is small This also motivates the author to an extended research in future when overcoming difficulties in accessing data, expanding to larger observation sample Some variables in the model have not achieved statistical significance such as institutional variables, human capital, and inflation Therefore, a future research is to study additional factors 24 for economic growth such as geopolitics, science and technology development, innovation, and political institutions to obtain insight understanding for developing economies with different political institutions such as China, Vietnam, and suitable with the world changing with Industrial Revolution 4.0 25 AUTHOR’S PUBLICATION 13) Phan Thị Bích Nguyệt & Phạm Dương Phương Thảo (2018) Limitation of Financial Development in Asian countries Banking Science and Training Review , No 199December/2018 14) Phan Thị Bích Nguyệt & Phạm Dương Phương Thảo (2018) Threshold of Financial Development enhancing Economic Growth sustainably for Asian countries Review of Finance, Volume 2-December/2018 15) Phạm Dương Phương Thảo (2018) Effects of Financial Development threshold to Economic Growth in Asian developing countries National Conference Proceedings 2018 “Accounting – Auditing – Finance in Vitenam: Current situation and solutions”, Finance Press, ISBN: 978-604-79-1828-7 16) Phạm Dương Phương Thảo (2018), Application of threshold model to effects of financial development to economic growth Science Conference Proceedings “Models in Finance: Theory & Practice”, UEH Publishing House, ISBN: 978-604-922-641-0 17) Phan Thị Bích Nguyệt & Phạm Dương Phương Thảo (2016) Economic growth and Financial Development in Asian developing countries Journal of Development and Intergration, 28(38), 69-74 Research at University level (2015), member, “Effects of financial development to economic growth: Empirical study in Vietnam and some Asian countries” – Accepted with ranking of Good ... biệt Tăng trưởng kinh tế Phát triển kinh tế Tăng trưởng kinh tế điều kiện cần điều kiện đủ phát triển kinh tế Hai khái niệm dễ bị nhầm lẫn cần phân biệt rõ Phát triển kinh tế mang nội hàm rộng tăng. .. vốn kinh tế thơng qua phát triển hệ thống tài tác động đến tăng trưởng kinh tế quốc gia 2.4 Bằng chứng thực nghiệm tác động Phát triển tài đến Tăng trưởng kinh tế Tác động phát triển tài lên tăng. .. hình tăng trưởng khác 2.1.3 Đo lường tăng trưởng kinh tế Tăng trưởng kinh tế tăng thu nhập quốc gia Vì vậy, hai chỉ số dùng để đo lường tăng trưởng kinh tế GDP GNP Để đo lường tăng trưởng kinh tế