I denna studie försöker vi finna svar på hur en praktisk lärardemonstration kan utföras på ett pedagogiskt vis. Vi undersöker även övergången från den stund som domineras av läraren till den stund som utmärks av individuellt elevarbete. Skolämnet som studien utgår ifrån är slöjd men vi tror att de utmaningar och resultat som framkommer kan appliceras även på andra skolämnen. Från svar på enkäter riktade till elever och intervjuer utförda med både lärare och elever framkommer att ett flertal aspekter spelar in för ett framgångsrikt lärande knutet till  demonstrationer. Lärarens kapacitet och förmåga att både förbereda och framföra något är viktig. Samtidigt spelar lärarens kontakt med och kunskap om, både grupp och individ, roll. Återkoppling till elever bör ske med fokus på det som utförts och som eleven kan påverka. Även faktorer av mer praktiska slag påverkar, som vid vilken tid på dagen lektionen pågår och om eleverna då är pigga eller ofokuserade. Att få demonstrationen och det efterkommande elevarbetet att vara en lärorik stund istället för något tråkigt är en utmanande, komplex och rolig del av läraryrket. Att lyckas med det kan vara avgörande för elevernas förståelse och lust att engagera sig i ämnet. / In this study we try to find answers on how a practical demonstration, performed by a teacher, can be conducted in both effective and pedagogic ways. We also explore the transition from a teacher lead period to a period defined by practical work and understanding performed by pupils. The subject studied is the swedish sloyd, but we think the challenges are mainly the same in any school subject. Through research on literature in areas such as rhetorics, leadership and pedagogy we contrast different aspects on the subject with surveys conducted on pupils and interviews with both pupils and teachers. From empirics we conclude that different aspects play important roles in succeeding with bringing a sloyd demonstration into individual pupil knowledge. The teacher’s capacity in preparation and enthralling an audience as well as his or her empathy and knowledge of the mental constitution of the class all play a part. It is also important how well the teacher gives individualized feedback, when pupils start working or no longer do work due to various reasons. Practical factors such as hour of the day and whether the pupils are alert or hungry also do contribute.  Bringing a demonstration from a dull experience into engaged pupil work is a challenging, complex and enjoyable part of a lesson. It may be crucial to the pupil’s future effort making and understanding.

The main objective of the study was to determine the exchange rate volatility regime for carry trade profitability when using the South African Rand as the target currency. The study used the Logistic Smooth Transition Regression (LSTR) model to test the uncovered interest rate parity (UIP). The Sharpe ratio and the risk adjusted forward premium were used as the transition variables. The transition variable is a function of the transition function, which is used to determine the regime for the UIP. The LSTR model is characterised by three regimes, i.e. the lower regime, the middle regime and the upper regime. The LSTR model was tested for the short-term forward rate maturity of less than one year. The results show that the UIP hypothesis holds in the middle regime for the Rand/USD and the Rand/GBP when using the Sharpe ratio as the transition variable. Meanwhile, the UIP hypothesis does not hold for the Rand/Yen when using the Sharpe ratio as the transition variable for the forward rate maturity of one month, and it does hold for other short-term forward rate maturity of less than one year. The results for the risk adjusted forward premium as the transition variable show that the UIP hypothesis does not hold for all three currencies at various short-term forward rate maturities of less than one year. The research provides the following contributions to new knowledge: (1) Uncovered interest parity hypothesis holds in the middle regime for all periods for the Rand/USD and the Rand/GBP when using the Sharpe ratio as the transition variable with a short-term forward rate maturity of less than one year. (2) Currency carry trade profit taking for the Rand/USD and the Rand/GBP can be achieved in the upper regime. (3) The results for the Rand/Yen are mixed, in that the UIP hypothesis does not hold for other crisis periods as a result of negative Sharpe ratios. However, for the calm periods, UIP hypothesis holds in the middle regime for the Rand/Yen for short-term forward rate maturity of more than one month but less than one year when using the Sharpe ratio as the transition variable. The overall contribution of this study is that for the South African Rand as the target currency, the UIP hypothesis holds for the short-term horizon when using the Sharpe ratio as the transition variable and that this mostly depends more on currency than on horizon. Contrary to other researchers who found that the UIP holds in the long-term maturity with higher Sharpe ratios in the upper regime, this study proved that the UIP holds in the short-term maturity horizon. / Business Management / D.B.L.

Η παρούσα διατριβή ασχολείται με δύο ιδιαιτέρως σημαντικά και διαχρονικά επίκαιρα ζητήματα στην ανάλυση χρονολογικών σειρών, τα οποία εντάσσονται, υπό ευρεία έννοια, στο πεδίο της Μακροοικονομετρίας. Ειδικότερα, μελετώνται θέματα και μεθοδολογίες ή τεχνικές ιδιαίτερα χρήσιμες για εκείνους τους ερευνητές, οι οποίοι επικεντρώνονται στην ανάλυση της συμπεριφοράς των συναθροιστικών (aggregate) μεγεθών της οικονομίας, βασιζόμενοι στη χρήση δεδομένων χρονοσειρών ή πιο απλά χρονοσειρές (time series). Το πρώτο ζήτημα αφορά στη μελέτη της δυναμικής αλληλεξάρτησης ανάμεσα σε μακροοικονομικές μεταβλητές κάτω από την υιοθέτηση ενός πολλαπλού πλαισίου ανάλυσης χρονοσειρών. Το ενδιαφέρον εστιάζεται κυρίως στην γενικευμένη ή εκτεταμένη έννοια της αιτιότητας κατά Granger, δηλαδή στην επέκταση της τυπικής έννοιας της αιτιότητας κατά Granger σε μεγαλύτερους του ενός ή σε πολλαπλούς ορίζοντες πρόβλεψης. Το δεύτερο ζήτημα αφορά στην παρουσία μη-γραμμικών χαρακτηριστικών σε μακροοικονομικές χρονοσειρές, καθώς και την υποδειγματοποίηση της μη-γραμμικότητας με τη χρήση μη-γραμμικών οικονομετρικών μοντέλων. Επικεντρώνεται δε ιδιαίτερα στον έλεγχο μοναδιαίας ρίζας κάτω από την εναλλακτική υπόθεση της στασιμότητας γύρω από μη-γραμμικές τάσεις της μορφής τάσεων ομαλής μετάβασης (smooth transition trends) στις μακροοικονομικές χρονοσειρές. Ουσιαστικά, η διατριβή διακρίνεται σε δύο κεφάλαια. Στο Κεφάλαιο 1 παρουσιάζεται η τυπική έννοια της αιτιότητας κατά Granger, καθώς και η γενικευμένη ή εκτεταμένη έννοια της αιτιότητας ή η αιτιότητα σε πολλαπλούς ορίζοντες (multi-horizon causality), στο πλαίσιο των διανυσματικών αυτοπαλίνδρομων υποδειγμάτων (VAR). Η τυπική έννοια της αιτιότητας κατά Granger περιορίζεται στη βελτίωση της προβλεψιμότητας σε ορίζοντα πρόβλεψης μίας περιόδου (one-step ahead), ενώ λαμβάνει υπ'όψιν μόνο τις άμεσες ροές πληροφόρησης μεταξύ των μεταβλητών ενδιαφέροντος (direct causality). Ωστόσο, σε υποδείγματα VAR με περισσότερες από δύο μεταβλητές η τυπική έννοια της αιτιότητας μπορεί να επεκταθεί με την μελέτη της βελτίωσης της προβλεψιμότητας σε μεγαλύτερους του ενός ορίζοντες πρόβλεψης. Σε μία περίπτωση όπως η τελευταία, πλην της άμεσης αιτιότητας, δύνανται να μελετηθούν και οι έμμεσες σχέσεις αιτιότητας (indirect causality) που ενδέχεται να προκύψουν μέσω των πρόσθετων μεταβλητών του συστήματος. Το θεωρητικό πλαίσιο της γενικευμένης έννοιας της αιτιότητας που παρουσιάζει η παρούσα διατριβή έχει αναπτυχθεί από τους Dufour and Renault (1998). Παράλληλα, δίνεται ιδιαίτερη βαρύτητα σε δύο πρόσφατες μεθόδους στατιστικής επαγωγής αιτιωδών σχέσεων κατά Granger σε πολλαπλούς ορίζοντες, οι οποίες παρέχουν πρόσθετη πληροφόρηση σχετικά με τη δυναμική αλληλεξάρτηση οικονομικών χρονοσειρών, και πιο συγκεκριμένα σχετικά με τον άμεσο ή έμμεσο χαρακτήρα των αιτιωδών σχέσεων, το διαχωρισμό μεταξύ βραχυχρόνιας και μακροχρόνιας (μη)-αιτιότητας, καθώς και τις πιθανές χρονικές υστερήσεις της αιτιότητας. Τέλος, στα πλαίσια του Κεφαλαίου 1, ερευνάται η δυνατότητα εφαρμογής των μεθόδων αυτών μέσω εμπειρικών εφαρμογών πάνω σε δύο διαχρονικά ζητήματα αιτιωδών σχέσεων ανάμεσα σε οικονομικές μεταβλητές. Στο Κεφάλαιο 2 παρουσιάζονται υποδείγματα ομαλής μετάβασης, καθώς και έλεγχοι μοναδιαίας ρίζας οι οποίοι επιτρέπουν την στασιμότητα γύρω από ομαλές ή βαθμιαίες μεταβάσεις κάτω από την εναλλακτική υπόθεση. Κύριο χαρακτηριστικό των υποδειγμάτων ομαλής μετάβασης είναι η παρουσία μη-γραμμικών τάσεων στη διαχρονική εξέλιξη των χρονοσειρών. Κεντρικό ρόλο στα υποδείγματα αυτά κατέχουν οι διαρθρωτικές μεταβολές (structural changes) στην προσδιοριστική τάση, οι οποίες, δεδομένου ότι αντιπροσωπεύουν μεταβολές της συναθροιστικής συμπεριφοράς, υποδειγματοποιούνται με τη χρήση ενός προσδιοριστικού στοιχείου το οποίο επιτρέπει την βαθμιαία αντί της στιγμιαίας προσαρμογής. Οι έλεγχοι μοναδιαίας ρίζας, οι οποίοι επιτρέπουν περισσότερη ευελιξία στην συνάρτηση της τάσης σε σχέση με την γραμμική εξειδίκευση της προσδιοριστικής τάσης που χρησιμοποιούν οι τυπικοί έλεγχοι μοναδιαίας ρίζας, αποτελούν το επίκεντρο μελέτης του Κεφαλαίου 2 της διατριβής. Η αναγκαιότητα υιοθέτησης πρόσθετων ελέγχων μοναδιαίας ρίζας, όπως οι έλεγχοι μοναδιαίας ρίζας οι οποίοι επιτρέπουν στασιμότητα γύρω από ομαλές μεταβάσεις κάτω από την εναλλακτική υπόθεση, ισχυροποιείται από τα αποτελέσματα της εφαρμογής των ελέγχων αυτών σε ένα σύνολο οικονομικών χρονοσειρών. / This thesis discusses two central research topics in applied time series econometrics that generally belong in the field of Macroeconometrics. In particular, we investigate issues and methods which are of interest to those researchers who want to analyze economic problems or economic aggregates by means of time series data. The first topic deals with the dynamic interrelationships between sets of theory related variables in a multiple time series context. Research interest is primarily focused on the generalized or extended notion of Granger causality, that is the extension of the standard Granger causality concept to higher forecast horizons. The second topic deals with nonlinear behavior of macroeconomic time series, as well as the modelling of nonlinearities in economic time series using nonlinear econometric models. Specific attention is paid to unit root tests that allow stationarity around nonlinear trends in the form of smooth transitions under the alternative. The dissertation consists of two chapters. The first chapter presents the standard concept of Granger causality, along with the generalized or extended notion of causality, also known as multiple-horizon causality, in the vector autoregressive (VAR) framework. The standard notion of Granger causality restricts prediction improvement to a forecast horizon of one period, while it considers only direct flows of information between the variables of interest. However, in VAR models with more than two variables, the concept of standard Granger causality can be extended by studying prediction improvement at forecast horizons greater than one. If this is the case, then, except for direct causality, indirect flows of information might be revealed through the additional variables of the system. The theoretical framework of the extended concept of causality which is presented in the present dissertation has been developed by Dufour and Renault (1998). In addition, special attention is paid to two recent methods for testing hypothesis of non-causality at various horizons which can provide further information on the dynamic interaction of time series, and more specifically on the direct or indirect nature of causal effects, the distinction between short-run and long-run (non)-causality, as wells as the possibility of causal delays. Finally, the potential implementation of these methods is examined through empirical applications on causality relations among different sets of economic variables. Chapter 2 presents smooth transition (STR) trend models, as well as unit root tests that allow stationarity around smooth transitions under the alternative. Smooth transition regression models presume the presence of nonlinear trends in the long-run evolution of time series. A key feature of these models is the presence of structural changes in the deterministic trend which, given that they represent changes in aggregate behavior (economic aggregates), are modelled through a deterministic component that permits gradual rather than instantaneous adjustment between regimes. Unit root tests that permit a more versatile trend function in the unit root procedure, rather than the standard linear trends, are the main concern of Chapter 2. The necessity of employing additional unit root tests, such as unit root tests that allow stationarity around smooth transitions under the alternative, becomes evident through the unit root test results that are observed in an application in a set of economic time series.

The thesis tries to explain different nature of the dynamics during the upward and downward part of the last house price cycle in Spain, characterized by important rigidities. Covered bonds are introduced as an instrument which may accelerate a house price boom, while it may also serve as a source of correction to overvalued house prices in downturn. In a serious economic stress, lack of investment opportunities motivates investors to buy the covered bonds due to the strong guarantees provided, which may in turn help to revitalize the credit and housing markets. To address such regime shift, house price dynamics is modelled within a framework of mutually related house price, credit and business cycles using smooth transition vector autoregressive model. Linear behaviour of such system is rejected, indicating the need to model house prices in a nonlinear framework. Also, importance of modelling house prices in the context of credit and business cycles is confirmed. Possible causality from issuance of covered bonds to house price dynamics was identified in this nonlinear structure. Finally, threat to financial stability resulting from rising asset encumbrance both in the upward and downward part of the house price cycle was identified, stressing the need to model impact of the covered bonds on house prices in...

La question de la transmission internationale des cycles a reçu une attention considérable en raison de l’intensification de la globalisation économique et financière. La problématique générale de cette thèse s’inscrit dans le prolongement de la littérature consacrée à cette question. Plus précisément, elle focalise son attention sur l’analyse de la transmission du cycle des Etats-Unis sur les pays émergents. Elle comporte trois chapitres. Le premier, en se basant sur une nouvelle approche économétrique en termes de modèle Global VAR, s’attache à étudier l’effet des chocs provenant des Etats-Unis sur les pays émergents. Il confirme l’idée que les Etats-Unis jouent un rôle important dans la transmission des cycles économiques étant donné leur poids dans l’économie mondiale. Le second chapitre propose d’étudier la transmission financière des Etats-Unis en s’intéressant à la crise des subprimes sur ces pays. L’estimation du modèle switch à probabilité variée développée indique que la persistance des stress financiers, le durcissement des conditions du crédit et l’augmentation du risque de non-solvabilité bancaire ont été les causes fondamentales de la transmission financière. La volatilité de l’indice boursier américain a été le facteur clé de la contamination avec tous les pays étudiés. Le troisième chapitre est consacré à étudier si les pays émergents sont en mesure d’adopter des politiques budgétaires contracycliques pouvant atténuer les chocs provenant de l’extérieur. En utilisant le modèle à seuil avec transition lisse en panel (le modèle PSTR), ce chapitre confirme que la politique budgétaire dans les pays émergents est procyclique en période de ralentissement économique et aussi lorsque la dette publique dépasse le seuil critique. De ce fait, une solide position budgétaire est fondamentale pour assurer la stabilité macroéconomique. / The issue of international transmission cycles has considerably received attention due to the increasing economic and financial globalization. Our thesis is in line with the literature dedicated to this question. More specifically, we focusour attention on the analysis of the transmission cycle of the United States to emerging countries. It consists of three chapters. The first one, based on a new econometric approach in terms of Global VAR model, aims to study the effect of shocks from the U.S. to emerging countries. The main resultconfirms the idea that the United States plays an important role in the transmission of economic cycles given their weight in the world economy. The second chapter proposes to study the financial transmission of the United States by focusing on the subprime crisis on these countries. The estimation of time varyingtransitionprobability (TVTP) Markov switchingmodel indicates that the persistence of financial stress, the tightening of the conditions of the credit and the increase of the risk of Banking solvency constitute the major determinants of the financial transmission. The US stock market volatility is the key factor transmission channel for all the studied countries. The third chapter is devoted to investigate whether emerging countries are able to adopt countercyclical fiscal policies to mitigate the impact from outside. Using the threshold model with smooth transition panel ( the PSTR model ), this chapter confirms that fiscal policy in emerging countries is procyclicalin the slowdown periodand also when public debt exceeds the critical threshold. Therefore, a strong fiscal position is fundamental to ensure macroeconomic stability.

The main objective of the study was to determine the exchange rate volatility regime for carry trade profitability when using the South African Rand as the target currency. The study used the Logistic Smooth Transition Regression (LSTR) model to test the uncovered interest rate parity (UIP). The Sharpe ratio and the risk adjusted forward premium were used as the transition variables. The transition variable is a function of the transition function, which is used to determine the regime for the UIP. The LSTR model is characterised by three regimes, i.e. the lower regime, the middle regime and the upper regime. The LSTR model was tested for the short-term forward rate maturity of less than one year. The results show that the UIP hypothesis holds in the middle regime for the Rand/USD and the Rand/GBP when using the Sharpe ratio as the transition variable. Meanwhile, the UIP hypothesis does not hold for the Rand/Yen when using the Sharpe ratio as the transition variable for the forward rate maturity of one month, and it does hold for other short-term forward rate maturity of less than one year. The results for the risk adjusted forward premium as the transition variable show that the UIP hypothesis does not hold for all three currencies at various short-term forward rate maturities of less than one year. The research provides the following contributions to new knowledge: (1) Uncovered interest parity hypothesis holds in the middle regime for all periods for the Rand/USD and the Rand/GBP when using the Sharpe ratio as the transition variable with a short-term forward rate maturity of less than one year. (2) Currency carry trade profit taking for the Rand/USD and the Rand/GBP can be achieved in the upper regime. (3) The results for the Rand/Yen are mixed, in that the UIP hypothesis does not hold for other crisis periods as a result of negative Sharpe ratios. However, for the calm periods, UIP hypothesis holds in the middle regime for the Rand/Yen for short-term forward rate maturity of more than one month but less than one year when using the Sharpe ratio as the transition variable. The overall contribution of this study is that for the South African Rand as the target currency, the UIP hypothesis holds for the short-term horizon when using the Sharpe ratio as the transition variable and that this mostly depends more on currency than on horizon. Contrary to other researchers who found that the UIP holds in the long-term maturity with higher Sharpe ratios in the upper regime, this study proved that the UIP holds in the short-term maturity horizon. / Business Management / D.B.L.

本文研究台灣貨幣需求結構改變，我們研究「變數」值(Piecewise in Variable)的結構轉折而非「時間」值(Piecewise in Time)，因為轉折點只是轉折區間的特例，所以本文建立一「變數模糊時間序列」(Fuzzy Time Series in Variable)模型來探討「變數的轉折區間」，相較於傳統時間序列研究方法如：時間序列模型、門檻轉折點模型與模糊時間序列模型等，本文所建立的變數模糊時間序列模型，所求取的股價轉折區間，不僅可改善對稱模型殘差項的非隨機現象，同時也改善了門檻轉折模型之轉折點股價指數太低的現象，並且有效地將轉折點變更為較一般化的轉折區間，足見本文所提出變數模糊時間序列模型在結構轉折的偵測上具有相對優勢，詳述如下： （一）、相較於對稱模型方面：變數模糊時間序列模型可避免對稱模型估計貨幣需求函數所產生的偏差，並且有效改善其殘差項具有非白噪音現象。 （二）、相較於門檻轉折模型方面：1.變數模糊時間序列模型較能有效驗證以下假說：貨幣需求的股價指數彈性在高股價區時較大，以及貨幣需求的所得彈性在高股價區時較小。2.變數模糊時間序列模型所求出的股價指數轉折區間水準值，對央行目前及未來貨幣政策較具實用性，3. 變數模糊時間序列模型再預測貨幣需求時，未如門檻轉折模型產生高估的偏誤。 （三）、相較於傳統模糊時間序列模型方面：變數模糊時間序列模型已改善傳統模糊時間序列模型的結構轉折區間太長之不合理現象。 （四）、相較於以「時間」為轉折的傳統時間序列模型方面：當貨幣需求函數的重要解釋變數在短時間持續發生較大幅度變化時，傳統時間序列模型可能無法診斷出結構轉變的缺失，本文的變數模糊時間序列模型可避免此一缺失。 （五）、在政策的應用上： 1. 中央銀行若未將資料，區分高低股價指數來分段估計貨幣需求函數，將使貨幣需求的所得彈性抑或是狹義貨幣需求的股價指數彈性的估計，產生頗大的偏誤。 2. 經建會在計算台灣地區的景氣對策信號中，其金融面指標同時包括有M1B貨幣供給的增加率與股價指數變動率，如此將造成在高股價指數下，股價指數上揚時高估了台灣地區的景氣狀況，而在股價指數下降時，則反之。 另外，由於台灣欠缺貨幣需求函數的重要解釋變數「所得」的月資料，以往文獻以工業生產指數等為替代變數以估計月貨幣需求函數，本文不僅證明這些方法的缺失，並提出「模糊距離權數法」來估計出月國內生產毛額資料，此一資料不僅可避免月工業生產指數等方法的三項缺失，而且在貨幣需求的估計上與預測上均有較佳的表現。 / Whether the ”money demand function” makes “structural change” happened or not ,that is crucial research for the monetary theory field. Therefore, many foreign and domestic papers have ever made studies on this. There have two major methods of study structural change. The first method is piecewise in time that is so popular and so many lecture study by it e.g. Juda and Scadding(1982), Shen(1999) ,Lin and Huang(1999),etc . Tsay(1989) had proposed a new methoed that is piecewise in variable . Distinct situation is suitable in using the two methods .We have two reasons to use the new method to study the structural change of Taiwan’s money demand function. First one is that Friedman(1988,Paul（1992）,Wu and Shea（1993）and Shen(1996) find the trade-volume of stock market or stock price are the important factors of money demand function. TSE is 12495 in February of 1990 and 2573 in October of 1990. TSE is changing so huge but all the Papers of piecewise in time can’t detect the structural change of Taiwan money demand. The second reason is that to detect the ” interval of financial variable” of structural change of Taiwan money demand is more benefit to the Central Bank than to detect the ” past time point” of structural change.　To detect the ” interval of financial variable” of structural change of Taiwan money demand is much convenient matters for monetary policy of Center Bank from now and future. Our research propose “fuzzy time series in variable” try to find the ” smoothing interval of financial variable” of structural change of money demand . Our method has two major benefits as follow: 1. Difference to TAR model: The TAR model find out the ” point of financial variable” of structural change. It seems metaphorically money demand function’s structural change suddenly. Our method find out the ” interval of financial variable” of structural change .It’s more reasonable that structural change of money demand function is gradually. 2. Difference to STAR model: So many STAR（Smooth Transition Autoregressive ）papers also find out the Gradual Transition Interval .For example: Terasvirta and Anderson(1992), Sarantis(1999) etc. But those lectures have the following point on why our method can improve it (a).STAR is piecewise in time. (b). STAR investigate structural change by just one variable AR process. But economists concern the structural change of variables. (c). The power of STAR to detect structural change is too weak. 3. We propose new summation average entropy formula that can improve the interval of structural change too longer.

[pt] A seleção de variáveis em modelos estatísticos é um problema importante, para o qual diferentes soluções foram propostas. Tradicionalmente, pode-se escolher o conjunto de variáveis explicativas usando critérios de informação ou informação à priori, mas o número total de modelos a serem estimados cresce exponencialmente a medida que o número de variáveis candidatas aumenta. Um problema adicional é a presença de mais variáveis candidatas que observações. Nesta tese nós estudamos diversos aspectos do problema de seleção de variáveis. No Capítulo 2, comparamos duas metodologias para regressão linear: Autometrics, que é uma abordagem geral para específico (GETS) baseada em testes estatísticos, e LASSO, um método de regularização. Diferentes cenários foram contemplados para a comparação no experimento de simulação, variando o tamanho da amostra, o número de variáveis relevantes e o número de variáveis candidatas. Em uma aplicação a dados reais, os métodos foram comparados para a previsão do PIB dos EUA. No Capítulo 3, introduzimos uma metodologia para seleção de variáveis em modelos regressivos e autoregressivos de transição suave (STR e STAR) baseada na regularização do LASSO. Apresentamos uma abordagem direta e uma escalonada (stepwise). Ambos os métodos foram testados com exercícios de simulação exaustivos e uma aplicação a dados genéticos. Finalmente, no Capítulo 4, propomos um critério de mínimos quadrados penalizado baseado na penalidade l1 do LASSO e no CVaR (Conditional Value at Risk) dos erros da regressão out-of-sample. Este é um problema de otimização quadrática resolvido pelo método de pontos interiores. Em um estudo de simulação usando modelos de regressão linear, mostra-se que o método proposto apresenta performance superior a do LASSO quando os dados são contaminados por outliers, mostrando ser um método robusto de estimação e seleção de variáveis. / [en] Variable selection in statistical models is an important problem, for which many different solutions have been proposed. Traditionally, one can choose the set of explanatory variables using information criteria or prior information, but the total number of models to evaluate increases exponentially as the number of candidate variables increases. One additional problem is the presence of more candidate variables than observations. In this thesis we study several aspects of the variable selection problem. First, we compare two procedures for linear regression: Autometrics, which is a general-to-specific (GETS) approach based on statistical tests, and LASSO, a shrinkage method. Different scenarios were contemplated for the comparison in a simulation experiment, varying the sample size, the number of relevant variables and the number of candidate variables. In a real data application, we compare the methods for GDP forecasting. In a second part, we introduce a variable selection methodology for smooth transition regressive (STR) and autoregressive (STAR) models based on LASSO regularization. We present a direct and a stepwise approach. Both methods are tested with extensive simulation exercises and an application to genetic data. Finally, we introduce a penalized least square criterion based on the LASSO l1- penalty and the CVaR (Conditional Value at Risk) of the out-of-sample regression errors. This is a quadratic optimization problem solved by interior point methods. In a simulation study in a linear regression framework, we show that the proposed method outperforms the LASSO when the data is contaminated by outliers, showing to be a robust method of estimation and variable selection.

Cette thèse de doctorat composée de trois chapitres contribue au développement de tests statistiques et à analyser la transmission financière dans un cadre multivarié hétéroscédastique. Le premier chapitre propose deux tests du multiplicateur de Lagrange de constance des corrélations conditionnelles dans les modèles GARCH multivariés. Si l'hypothèse nulle repose sur des corrélations conditionnelles constantes, l'hypothèse alternative propose une première spécification basée sur des réseaux de neurones artificiels et une seconde représentée par une forme fonctionnelle inconnue qui est linéarisée à l'aide d'un développement de Taylor.Dans le deuxième chapitre, un nouveau modèle est introduit dans le but de tester la non-linéarité des (co)variances conditionnelles. Si l'hypothèse nulle repose sur une fonction linéaire des innovations retardées au carré et des (co)variances conditionnelles, l'hypothèse alternative se caractérise quant à elle par une fonction de transition non-linéaire : exponentielle ou logistique ; une configuration avec effets de levier est également proposée. Dans les deux premiers chapitres, les expériences de simulations et les illustrations empiriques montrent les bonnes performances de nos tests de mauvaise spécification.Le dernier chapitre étudie la transmission d'information en séance et hors séance de cotation en termes de rendements et de volatilités entre la Chine, l'Amérique et l'Europe. Le problème d'asynchronicité est considéré avec soin dans la modélisation bivariée avec la Chine comme référence. / This Ph.D. thesis composed by three chapters contributes to the development of test statistics and to analyse financial transmission in a multivariate heteroskedastic framework.The first chapter proposes two Lagrange multiplier tests of constancy of conditional correlations in multivariate GARCH models. Whether the null hypothesis is based on constant conditional correlations, the alternative hypothesis proposes a first specification based on artificial neural networks, and a second specification based on an unknown functional form linearised by a Taylor expansion.In the second chapter, a new model is introduced in order to test for nonlinearity in conditional (co)variances. Whether the null hypothesis is based on a linear function of the lagged squared innovations and the conditional (co)variances, the alternative hypothesis is characterised by a nonlinear exponential or logistic transition function; a configuration with leverage effects is also proposed.In the two first chapters, simulation experiments and empirical illustrations show the good performances of our misspecification tests.The last chapter studies daytime and overnight information transmission in terms of returns and volatilities between China, America and Europe. The asynchronicity issue is carefully considered in the bivariate modelling with China as benchmark.