Submitted by Nicole de Mendonça Saba (nicolesaba@gmail.com) on 2015-09-24T17:21:52Z No. of bitstreams: 1 Nicole Saba versao final_vf.pdf: 1360650 bytes, checksum: aafa0056ed232ccdb36bda0393568740 (MD5) / Approved for entry into archive by Renata de Souza Nascimento (renata.souza@fgv.br) on 2015-09-24T17:28:57Z (GMT) No. of bitstreams: 1 Nicole Saba versao final_vf.pdf: 1360650 bytes, checksum: aafa0056ed232ccdb36bda0393568740 (MD5) / Made available in DSpace on 2015-09-24T17:33:40Z (GMT). No. of bitstreams: 1 Nicole Saba versao final_vf.pdf: 1360650 bytes, checksum: aafa0056ed232ccdb36bda0393568740 (MD5) Previous issue date: 2015-08-19 / Este trabalho procura identificar quais variáveis são as mais relevantes para previsão da taxa de câmbio real do Brasil e analisar a robustez dessas previsões. Para isso foram realizados testes de cointegração de Johansen em 13 variáveis macroeconômicas. O banco de dados utilizado são séries trimestrais e compreende o período de 1970 a 2014 e os testes foram realizados sobre as séries combinadas dois a dois, três a três e quatro a quatro. Por meio desse método, encontramos nove grupos que cointegram entre si. Utilizando esses grupos, são feitas previsões fora da amostra com a partir das últimas 60 observações. A qualidade das previsões foi avaliada por meio dos testes de Erro Quadrático Médio, teste de Diebold-Mariano e, além disso, foi utilizado um modelo de passeio aleatório do câmbio real como benchmark para o procedimento de Hansen. Todos os testes mostram que, à medida que se aumenta o horizonte de projeção, o passeio aleatório perde poder preditivo e a maioria dos modelos são mais informativos sobre o futuro da o câmbio real efetivo. O horizonte é de três a quatro anos à frente. No caso do teste de Hansen, o passeio aleatório é completamente eliminado do grupo final de modelos, mostrando que é possível fazer previsões superiores ao passeio aleatório. / This paper seeks to identify which variables are most relevant to forecast Brazil's real exchange rate and also analyze the robustness of the results. To that end, we conducted Johansen cointegration tests on 13 different variables. The database covers the period of 1970 to 2014 with quarterly frequency. The series were combined in subsets of two, three and four variables. After conducting the Johansen cointegration test, we found that nine different groups that are cointegrated. We then proceed to estimate out-of-sample forecasts of the real exchange rate for each of these nine groups. Once we have these forecasts, we evaluate their quality by calculating their mean squared errors and conduct the Diebold-Mariano Test. We also use a random walk model of the exchange rate as benchmark for Hansen's model confidence set. All of the tests show that, as we expand the forecast horizon, the random walk series' predictive power is far worse than the other forecasts. In the case of Hansen's model confidence set, the random walk series is eliminated from the final confidence set of models. The time horizon is three to four years, which gives us evidence of forecast accuracy gains superior to the random walk model for the exchange rate in the long term.

波松分配（Poisson Distribution）常用在單位時間或是區間內，計算對有興趣之某隨機事件次數（或是已知事件之頻率），例如：速食餐廳的單位時間來客數，又或是每段期間內，某天然災害的發生次數，可以表示為某一特定事件X服從波松分配，若lambda為單位事件發生次數或是平均次數，我們稱lambda為此波松分配之母數，記作Poisson(lambda)，其中lambda屬於實數。 今天我們若想要探討由兩個服從不同波松分配抽取的隨機變數，如下列所述：令X={(X1,X2)}為一集合，其中Xi為X(i,1),X(i,2),...,X(i,ni)~Poisson(lambda(i)),i=1,2。欲探討兩波松分配之均數是否相同或相差小於某個常數d時，考慮以下檢定:H0:lambda2-lambda1<=d與H0:lambda2-lambda1>d，對於此問題可以使用的檢定方法有Przyborwski和Wilenski(1940)提出的條件檢定（Conditional test,C-test）或K.Krishnamoorthy與Jessica Thomson(2002)提出的精確性檢定（Exact test,E-test），其中的精確性檢定為一個非條件檢定（Unconditional Test）；K.Krishnamoorthy與Jessica Thomson比較條件檢定與精確性檢定的p-value皆小於顯著水準(apha)，而精確性檢定的檢定力不亞於條件檢定，因此精確性檢定比條件檢定更適合上面所述之假設問題。 Roger L.Berger（1996）提出一個以信賴區間的p-value所建立的較強力檢定，而目前只用於檢定兩二項分配（Binomial Distribution）的機率參數p是否相同為例，然而Berger在文中提到，較強力檢定比非條件檢定有更好的檢定力，而且要求的計算時間較少，可以提升檢定的效率。 本篇論文我們希望在固定apha與d時檢定的問題，建立一個兩波松分配均數顯著水準為apha的較強力檢定。 利用Roger L.Berger與Dennis D.Boos(1994)提出以信賴區間的p-value方法，建立波松分配兩兩母均數差的較強力檢定；研究發現此較強力檢定與精確性檢定的p-value皆小於apha，然而我們的檢定的檢定力皆不亞於精確性檢定所計算得出的檢定力，然而其apha及虛無假設皆需要善加考慮以本篇研究來看，當檢定為單尾檢定時，若apha<0.01，我們的較強力檢定沒有辦法找到比精確性檢定更好地拒絕域，換言之，此時較強力檢定與精確性檢定的檢定力將會相等。 / Poisson Distribution is used to calculate the probability of a certain phenomenon which attracted by researcher. If we want to test two random variable in an experiment .Therefore ,let X={(X1,X2)} be independent samples ,respectively ,from Poisson distribution ,also X(i,1),X(i,2),...,X(i,ni)~Poisson(lambda(i)),i=1,2. The problem of interest here is to test: H0:lambda2-lambda1<=d and H0:lambda2-lambda1>d, where 0<apha<1/2 ,and let Y1 equals sum of X1 and Y2 equals sum of X2, where apha ,lambda,d be fixed. In this problem of hypothesis testing about two Poisson means is addressed by the conditional test.However ,the exact method of testing based on the test statistic considered in K.Krishnamoorthy,Jessica Thomson(2002) also commonly used. Roger L.Berger ,Dennis D.Boos(1994) give a new way to calculate p-value,which replace the old method ,called it a valid p-value .In 1996, Roger L.Berger used the new way to propose a new test for two parameter of binomial distribution which is more powerful than exact test. In the other hand, Roger L.Berger also explain the unconditional test is more suitable than the conditional test. In this paper,we propose a new method for two parameter of Poisson distribution which revise from Roger L.Berger’s method. The result we obtain that our new test is really get a much bigger rejection region.We found when the fixed increasing ,the set of more powerful test increasing, and when the fixed power increasing ,the required sample size decreasing.