• Journal of the Korean Statistical Society
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• v.26 no.2
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• pp.171-180
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• 1997

Effects of order misspecification on statistical behavior of unit root tests are studied. We derive the limiting distributions of the Dickey-Fuller test statistics whose numerators are of the form c .int. W dW + .kappa. where W is a standard Brownian motion on [0, 1] and c is a real number. The term .kappa. is a major consequence of order misspecification and its explict expression is derived. Based on an analysis of .kappa., effects of order misspecification on unit root tests for AR(2), ARMA(1, 1), and AR(3) models are investigated.

• Journal of Convergence for Information Technology
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• v.9 no.12
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• pp.54-61
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• 2019

Recently, IITS (intelligent integrated transportation system) has been important topic in Smart City related industry. As a main objective of IITS, prevention of traffic jam (due to car accidents) has been attempted with help of advanced sensor and communication technologies. Studies show that car accident has certain correlation with some factors including characteristics of location, weather, driver's behavior, and time of day. We concentrate our study on observing auto correlativity of car accidents in terms of time of day. In this paper, we performed the ARIMA tests including ADF (augmented Dickey-Fuller) to check the three factors determining auto-regressive, stationarity, and lag order. Summary on forecasting of hourly car crash counts is presented, we show that the traffic accident data obtained in Korea can be applied to ARIMA model and present a result that traffic accidents in Korea have property of being recurrent daily basis.

• Journal of the Korean Data and Information Science Society
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• v.25 no.2
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• pp.385-392
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• 2014

Random walk hypothesis is a hypothesis that explains theoretically the difficulty in forecasting in financial market. Various tests for the hypothesis have been developed so far but it is known that those tests suffer from low power and size distortion. In this article, a sign test based on slopes are suggested to overcome these difficulties. A simulation study is conducted to compare this test to the often used Dickey and Fuller (1979) test.

• The Korean Journal of Financial Studies
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• v.6 no.1
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• pp.313-334
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• 2000

In this paper, we obtained some supportive evidence for the long-run PPP relationship concerning the Korean Won currency. Previous tests of PPP in the bilateral exchange rates of the Korean Won rate vis-a-vis the U.S. Dollar have been exposed to the lack of power problem. We argue that their failure to find PPP relation in Korean Won rates was due to the low power of Augmented Dickey-Fuller tests or the Engle-Granger two-step tests applied to the Korean exchange rate data with short sample period. En attempting to alleviate this low power problem, we used the error-correction model test and the Johansen test for bilateral long-run equilibrium relationships between exchange rates and price indices from Korea's major trading partners. It is surprising that our evidence supporting for long-run PPP in Korean Won rate contrasts sharply with Bahmani-Oskooee, Moshen and Rhee, Hyun-Jae(1992)'s.

• Journal of the Korean Statistical Society
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• v.27 no.1
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• pp.57-66
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• 1998

In the analysis of time series it is an important issue to determine whether a time series under study is stationary. For the test of the stationary of the time series the Dickey-Fuller (DF) type tests have been mainly used. In this paper, we consider the regular unit root tests and seasonal unit root tests based on the generalized Durbin-Watson (DW) statistics when the errors are independent. The limiting distributions of the proposed DW-type test statistics are the functionals of standard Brownian motions. We also obtain the finite distributions and powers of the DW-type test statistics and compare the performances with the DF-type tests. It is observed that the DW-type test statistics have good behaviors against the DF-type test statistics especially in the nonzero (seasonal) mean model.

• Journal of Korean Society of Forest Science
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• v.89 no.1
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• pp.1-8
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• 2000

This paper investigates the empirical validity of market integration for the five softwood lumber markets in Canada : Atlantic, Quebec, Ontario, Prairie, and British Columbia (BC). The Augmented Dickey-Fuller (ADF) tests of monthly price series for the period 1987 : 10-1998 : 11 reveal strong evidence for the presence of a unit root in each series. Accordingly, the Johansen cointegration technique is used to test for the law of one price in the five regional markets. Results show that the law holds in the pair, three, four, and five markets, supporting the hypothesis of market integration.

• Journal of the Korean Statistical Society
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• v.24 no.2
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• pp.481-493
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• 1995

An ARIMA signal observed with measurement error is shown to have another ARIMA representation with nonlinear restrictions on parameters. For this model, the restricted Newton-Raphson estimator(RNRE) of the unit root is shown to have the same limiting distribution as the ordinary least squares estimator of the unit root in an AR(1) model tabulated by Dickey and Fuller (1979). The RNRE of parameters of the ARIMA(p,1,k) process and unit root tests base on the RNRE are developed.

• The Journal of Asian Finance, Economics and Business
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• v.7 no.10
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• pp.523-530
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• 2020

The efficient market hypothesis explains the random walk hypothesis suggesting that stock prices are independent of each other, hence, it is impossible to earn abnormal profits. The positive effect of a well-functioning and highly efficient stock market on the performance of an economy motivated the Philippine Stock Exchange to pursue massive modernization initiatives. This research provides evidence of the existence of random walk in the Philippine stock market employing the Augmented Dickey-Fuller (1981) and Phillips-Perron (1988) unit root tests, the Lo-MacKinlay's (1988) conventional variance ratio test, and Chow-Denning's (1993) simple multiple variance ratio test. Results of the ADF and PP unit root tests confirm the necessary condition for a random walk. The Chow-Denning (1993) maximum /z/ statistic and the Wald test statistic as in Richardson and Smith (1991) for the joint hypotheses and the Lo and MacKinlay (1988) individual statistics variance ratio test generally accepted the null hypothesis of a random walk. That is, the unit root and variance ratio tests consistently indicate that the null hypothesis of random walk cannot be rejected. The existence of a random walk in weak-form efficiency can be attributed to market liquidity as a result of continuous development and modernization of the Philippine equity market.

• Journal of the Korean Data and Information Science Society
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• v.25 no.6
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• pp.1499-1506
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• 2014

Random walk is used for describing random phenomenon in various areas but tests for random walk developed so far are known to suffer from size distortion and low power. Kim et al. (2014) proposed a sign test for unit root (${\rho}=1$) hypothesis based on slopes. This article proposes a Wilcoxon signed rank test based on slopes for unit root hypothesis, and compares it with the augmented Dickey-Fuller test and the sign test by a simulation study. Our results confirm that the nonparametric tests are better than ADF test for small samples like n = 30. The results also show that the sign test is better than the Wilcoxon signed rank test and that for 0 < ${\rho}$ < 1 (-1 < ${\rho}$ < 0), the nonparametric tests suffer from power loss (improvement) as normal error changes to double exponential error.

• The Journal of Asian Finance, Economics and Business
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• v.7 no.12
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• pp.677-682
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• 2020

To investigate the nexus between urban population, gross capital formation, and economic growth in the Kingdom of Saudi Arabia, yearly data was collected from the World Bank for the period 1974- 2018. Basic statistics test and correlation matrix was used to investigate the causal effect among the tested parameters, followed by Augmented Dickey-Fuller (ADF) stationary test, co-integration analysis by Johansen test after that Vector Auto-Correction Model for both short-run and long-run and finally the Granger-Causality tests. Result of unit root test analysis shows that the urban population became stationary at I (0) level while economic growth and gross capital formation became stationary at I (1). Johansen co-integration analysis indicates that there is presence of both long-run and short-run relationship between the three variables in the Kingdom of Saudi Arabia. The result of the VECM Model reflects that both economic growth and gross capital formation have a negative impact on urban population in the short run. According to the Granger-Causality tests, there is unidirectional causality with the urban population by both gross capital formation and economic growth. Also, the result of the Granger Causality tests show that there is unidirectional causality between economic growth and gross capital formations.