| 1. |
-
- 2017
-
Ingår i: Physical Review D. - 2470-0010 .- 2470-0029. ; 96:2
-
Tidskriftsartikel (refereegranskat)
|
|
| 2. |
-
- 2019
-
Tidskriftsartikel (refereegranskat)
|
|
| 3. |
- Janko, Matthew R., et al.
(författare)
-
In situ bypass and extra-anatomic bypass procedures result in similar survival in patients with secondary aortoenteric fistulas
- 2021
-
Ingår i: Journal of Vascular Surgery. - : Elsevier. - 0741-5214 .- 1097-6809. ; 73:1, s. 210-221.e1
-
Tidskriftsartikel (refereegranskat)abstract
- Objective: The optimal revascularization modality in secondary aortoenteric fistula (SAEF) remains unclear in the literature. The purpose of this investigation was to determine the revascularization approach associated with the lowest morbidity and mortality using real-world data in patients with SAEF. Methods: A retrospective, multi-institutional study of SAEF from 2002 to 2014 was performed using a standardized database. Baseline demographics, comorbidities, and operative and postoperative variables were recorded. The primary outcome was long-term mortality. Descriptive statistics, Kaplan-Meier survival analysis, and univariate and multivariate analyses were performed. Results: During the study period, 182 patients at 34 institutions from 11 countries presented with SAEF (median age, 72 years; 79% male). The initial aortic procedures that resulted in SAEF were 138 surgical grafts (76%) and 42 endografts (23%), with 2 unknown; 102 of the SAEFs (56%) underwent complete excision of infected aortic graft material, followed by in situ (in-line) bypass (ISB), including antibiotic-soaked prosthetic graft (53), autogenous femoral vein (neoaortoiliac surgery; 17), cryopreserved allograft (28), and untreated prosthetic grafts (4). There were 80 patients (44%) who underwent extra-anatomic bypass (EAB) with infected graft excision. Overall median Kaplan-Meier estimated survival was 319 days (interquartile range, 20-2410 days). Stratified by EAB vs ISB, there was no significant difference in Kaplan-Meier estimated survival (P = .82). In comparing EAB vs ISB, EAB patients were older (74 vs 70 years; P = .01), had less operative hemorrhage (1200 mL vs 2000 mL; P = .04), were more likely to initiate dialysis within 30 days postoperatively (15% vs 5%; P = .02), and were less likely to experience aorta-related hemorrhage within 30 days postoperatively (3% aortic stump dehiscence vs 11% anastomotic rupture; P = .03). There were otherwise no significant differences in presentation, comorbidities, and intraoperative or postoperative variables. Multivariable Cox regression showed that the duration of antibiotic use (hazard ratio, 0.92; 95% confidence interval, 0.86-0.98; P = .01) and rifampin use at time of discharge (hazard ratio, 0.20; 95% confidence interval, 0.05-0.86; P = .03) independently decreased mortality. Conclusions: These data suggest that ISB does not offer a survival advantage compared with EAB and does not decrease the risk of postoperative aorta-related hemorrhage. After repair, <50% of SAEF patients survive 10-months. Each week of antibiotic use decreases mortality by 8%. Further study with risk modeling is imperative for this population. (J Vasc Surg 2021;73:210-21.)
|
|
| 4. |
- Janko, Matthew, et al.
(författare)
-
Contemporary Outcomes After Partial Resection of Infected Aortic Grafts
- 2021
-
Ingår i: Annals of Vascular Surgery. - : Elsevier. - 0890-5096 .- 1615-5947. ; 76, s. 202-210
-
Tidskriftsartikel (refereegranskat)abstract
- INTRODUCTION: Aortic graft infection remains a considerable clinical challenge, and it is unclear which variables are associated with adverse outcomes among patients undergoing partial resection.METHODS: A retrospective, multi-institutional study of patients who underwent partial resection of infected aortic grafts from 2002 to 2014 was performed using a standard database. Baseline demographics, comorbidities, operative, and postoperative variables were recorded. The primary outcome was mortality. Descriptive statistics, Kaplan-Meier (KM) survival analysis, and Cox regression analysis were performed.RESULTS: One hundred fourteen patients at 22 medical centers in 6 countries underwent partial resection of an infected aortic graft. Seventy percent were men with median age 70 years. Ninety-seven percent had a history of open aortic bypass graft: 88 (77%) patients had infected aortobifemoral bypass, 18 (16%) had infected aortobiiliac bypass, and 1 (0.8%) had an infected thoracic graft. Infection was diagnosed at a median 4.3 years post-implant. All patients underwent partial resection followed by either extra-anatomic (47%) or in situ (53%) vascular reconstruction. Median follow-up period was 17 months (IQR 1, 50 months). Thirty-day mortality was 17.5%. The KM-estimated median survival from time of partial resection was 3.6 years. There was no significant survival difference between those undergoing in situ reconstruction or extra-anatomic bypass (P = 0.6). During follow up, 72% of repairs remained patent and 11% of patients underwent major amputation. On univariate Cox regression analysis, Candida infection was associated with increased risk of mortality (HR 2.4; P = 0.01) as well as aortoenteric fistula (HR 1.9, P = 0.03). Resection of a single graft limb only to resection of abdominal (graft main body) infection was associated with decreased risk of mortality (HR 0.57, P = 0.04), as well as those with American Society of Anesthesiologists classification less than 3 (HR 0.35, P = 0.04). Multivariate analysis did not reveal any factors significantly associated with mortality. Persistent early infection was noted in 26% of patients within 30 days postoperatively, and 39% of patients were found to have any post-repair infection during the follow-up period. Two patients (1.8%) were found to have a late reinfection without early persistent postoperative infection. Patients with any post-repair infection were older (67 vs. 60 years, P = 0.01) and less likely to have patent repairs during follow up (59% vs. 32%, P = 0.01). Patients with aortoenteric fistula had a higher rate of any post-repair infection (63% vs. 29%, P < 0.01)CONCLUSION: This large multi-center study suggests that patients who have undergone partial resection of infected aortic grafts may be at high risk of death or post-repair infection, especially older patients with abdominal infection not isolated to a single graft limb, or with Candida infection or aortoenteric fistula. Late reinfection correlated strongly with early persistent postoperative infection, raising concern for occult retained infected graft material.
|
|
| 5. |
|
|
| 6. |
- Byusa, Vincent
(författare)
-
Money demand, real effective exchange rates, and uncertainty
- 2024
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This PhD thesis consists of three distinct but interrelated research papers that collectively explore critical aspects of money demand, real effective exchange rates behavior, and uncertainty in different contexts. The first paper examines the nature of money demand in Rwanda and the rationale for the country’s monetary policy shift to inflation targeting in 2019, providing evidence of long-run money demand stability despite uncertainties affecting the global economy, and challenging the view that monetary aggregates should have no role in Rwanda’s monetary policy. The second paper investigates the complex effects of grant revenues on real effective exchange rates in Sub-Saharan African countries, revealing the outcomes of short-run depreciation and long-run appreciation. The last paper assesses how exchange rate regime choice affects the degree and persistence of real effective exchange rate misalignments, showing that, relative to a floating exchange rate regime, fixed and intermediate regimes effectively limit misalignment size, although with higher persistence. Together, these papers offer nuanced insights into the interaction between the money market, uncertainty, external grants, and exchange rate regime, underscoring the need for careful policy consideration to ensure economic stability and competitive currency values.
|
|
| 7. |
|
|
| 8. |
- Hacker,, R Scott, 1964-, et al.
(författare)
-
A Bootstrap Test for Causality with Endogenous Lag Length Choice : theory and application in finance
- 2010
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Granger causality tests have become among the most popular empirical applications with time series data. Several new tests have been developed in the literature that can deal with different data generating processes. In all existing theoretical papers it is assumed that the lag length is known a priori. However, in applied research the lag length has to be selected before testing for causality. This paper suggests that in investigating the effectiveness of various Granger causality testing methodologies, including those using bootstrapping, the lag length choice should be endogenized, by which we mean the data-driven preselection of lag length should be taken into account. We provide and accordingly evaluate a Granger-causality bootstrap test which may be used with data that may or may not be integrated, and compare the performance of this test to that for the analogous asymptotic test. The suggested bootstrap test performs well and appears to be also robust to ARCH effects that usually characterize the financial data. This test is applied to testing the causal impact of the US financial market on the market of the United Arab Emirates.
|
|
| 9. |
- Hacker, R. Scott, et al.
(författare)
-
A bootstrap test for causality with endogenous lag length choice : theory and application in finance
- 2012
-
Ingår i: Journal of economic studies. - : Emerald. - 0144-3585 .- 1758-7387. ; 39:2, s. 144-160
-
Tidskriftsartikel (refereegranskat)abstract
- Purpose – In all existing theoretical papers on causality it is assumed that the lag length is known a priori. However, in applied research the lag length has to be selected before testing for causality. The purpose of this paper is to suggest that in investigating the effectiveness of various Granger causality testing methodologies, including those using bootstrapping, the lag length choice should be endogenized, by which we mean the data-driven preselection of lag length should be taken into account.Design/methodology/approach – The size and power of a bootstrap test with endogenized lag-length choice are investigated by simulation methods. A statistical software component is produced to implement the test, which is available online.Findings – The simulation results show that this test performs well. An application of the test provides empirical support for the hypothesis that the UAE financial market is integrated with the US market.Social implications – The empirical results based on this test are expected to be more precise.Originality/value – This paper considers a bootstrap test for causality with endogenous lag order. This test has superior properties compared to existing causality tests in terms of size, with similar if not better power and it is robust to ARCH effects that usually characterize financial data. Practitioners interested in causal inference based on time series data might find the test valuable.
|
|
| 10. |
- Hacker, R Scott, et al.
(författare)
-
A Test for Multivariate ARCH Effects
- 2005
-
Ingår i: Applied Economics Letters. - : Informa UK Limited. - 1350-4851 .- 1466-4291. ; 12:7, s. 411-417
-
Tidskriftsartikel (refereegranskat)abstract
- This paper extends Engle's LM test for ARCH affects to multivariate cases. The size and power properties of this multivariate test for ARCH effects in VAR models are investigated based on asymptotic and bootstrap distributions. Using the asymptotic distribution, deviations of actual size from nominal size do not appear to be very excessive. Nevertheless, there is a tendency for the actual size to overreject the null hypothesis when the nominal size is 1% and underreject the null when the nominal size is 5% or 10%. It is found that using a bootstrap distribution for the multivariate LM test is generally superior in achieving the appropriate size to using the asymptotic distribution when (1) the nominal size is 5%; (2) the sample size is small (40 observations) and/or the VAR system is stable. With a small sample, the power of the test using the bootstrap distribution also appears better at the 5% nominal size.
|
|
| 11. |
- Hacker, R Scott, et al.
(författare)
-
An Alternative Method to Test for Contagion with an Application to the Asian Financial Crisis
- 2005
-
Ingår i: Applied Financial Economics Letters. - : Informa UK Limited. - 1744-6546 .- 1744-6554. ; 1:6, s. 343-347
-
Tidskriftsartikel (refereegranskat)abstract
- This paper investigates the size properties of a test for contagion based on an asymptotic t -distribution. The simulations show that this asymptotic test does not have correct size properties. An alternative test method based on case-resampling bootstrapping is introduced to improve on the correctness of inference. The simulations show that this new test has much better size properties. It also has quite high power properties and it is robust to ARCH effects. The method is applied to testing for contagion from Thailand to Indonesia during the Asian financial crisis.
|
|
| 12. |
- Hacker, R. Scott, et al.
(författare)
-
An investigation of the causal relations between exchange rates and interest rate differentials using wavelets
- 2014
-
Ingår i: International Review of Economics and Finance. - : Elsevier BV. - 1059-0560 .- 1873-8036. ; 29, s. 321-329
-
Tidskriftsartikel (refereegranskat)abstract
- This paper uses wavelet analysis to investigate causality between the spot exchange rate and the nominal interest rate differential for seven country pairs, which includes Sweden. Impulse response functions are also utilized to examine the signs of how one of these variables affects the other over time. One key empirical finding from the causality tests is that there is strengthening evidence of the nominal interest rate differential Granger causing the exchange rate as the wavelet time scale increases. When considering impulse responses on how the interest rate differential affects the exchange rate, there appears to be some evidence of more negative relationships at the shorter time scales (i.e. an increase in the Swedish interest rate compared to that of another country is associated with a lower Swedish krona price of the other country's currency) and more positive relationships at the longer time scales.
|
|
| 13. |
- Hacker, R Scott, 1964-, et al.
(författare)
-
An Investigation of the Causal Relations between Exchange Rates and Interest Rates Differentials using Wavelets
- 2010
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Monthly and quarterly data for the spot exchange rate of the Swedish Krona against major currencies have been used in this paper to investigate the causality in a Granger sense at different time scales between the spot exchange rate and the nominal interest rate differential by using wavelet analysis. Impulse response functions are also utilized to examine the signs of how one of these variables affects the other over time. One key empirical finding from the causality tests is that there is only substantial evidence of a causal relationship in the long run between the two variables. When using monthly data, this is true in both directions. When considering impulse responses on how the interest rate differential affects the exchange rate, there appears to be some evidence of more negative relationships at the shorter time scales and more positive relationships at the longer time scales.
|
|
| 14. |
- Hacker, R Scott, et al.
(författare)
-
Capital Mobility in Sweden : A Time Varying Parameter Approach
- 2007
-
Ingår i: Applied Economics Letters. - : Informa UK Limited. - 1350-4851 .- 1466-4291. ; 14:15, s. 1115-1118
-
Tidskriftsartikel (refereegranskat)abstract
- This article investigates the degree of capital mobility in Sweden during 1993 to 2004 using quarterly data. A time varying parameter model is estimated by the Kalman filter, and it shows that the relationship between investment as share in gross domestic product (GDP) and saving as share in GDP is much less than one (within the interval of 0.25–0.35), indicating substantial capital mobility. However, since the coefficient in each period is statistically different from zero, capital is still not perfectly mobile. Nevertheless, capital mobility seems to have increased until 1995 when Sweden became a member of EU and after membership there seems to be no significant increase in capital mobility.
|
|
| 15. |
- Hacker, R. Scott, 1964-, et al.
(författare)
-
Commonalities in the levels and movements of the inflation rates among countries in the East African Community
- 2022
-
Ingår i: Emerging markets finance & trade. - : Taylor & Francis. - 1540-496X .- 1558-0938. ; 58:9, s. 2493-2504
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, we investigate the degree to which inflation rates and their movements for countries in the East African Community (EAC) have become more similar, which is an important issue for the EAC’s goal of creating a common currency. We find that the five EAC countries (excluding South Sudan) have had a tendency to converge in their inflation-rate levels, and we show through an inflation-movement similarity index that inflation-rate changes between consecutive months trended toward becoming more similar between 1995 and 2018 for most country pairs from these EAC countries. We also find that the inflation correlations between these EAC countries seem favorable for monetary union when comparing these correlations to analogous ones for the 2001 European Monetary Union countries prior to the creation of the euro and to analogous ones for the West African Economic Monetary Union countries.
|
|
| 16. |
|
|
| 17. |
- Hacker, R Scott, et al.
(författare)
-
How Productivity and Domestic Output Are Related to Exports and Foreign Output in the Case of Sweden
- 2003
-
Ingår i: Empirical Economics. - : Springer Science and Business Media LLC. - 0377-7332 .- 1435-8921. ; 28:4, s. 767-782
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper we examine the relationships between two sets of three variables: Swedish real exports, Swedish real GDP, and foreign real GDP in one set; and Swedish real exports, Swedish total factor productivity, and foreign real GDP in the other set. The foreign real GDP facing Sweden is proxied by total OECD real GDP minus Sweden's real GDP. Multivariate tests for integration and cointegration show that the variables in each model are cointegrated. We also perform Granger causality tests on these variables in our examination using the Toda-Yamamoto procedure. We discover bi-directional causality between Swedish real exports and Swedish real GDP (or Swedish total factor productivity). Foreign real GDP is shown to Granger cause Swedish real exports, but no significant causation of foreign real GDP on either domestic GDP or total factor productivity was found. A change in foreign real GDP thus appears to affect Swedish output and productivity only indirectly, through changes in Swedish exports.
|
|
| 18. |
- Hacker, R Scott, et al.
(författare)
-
Is the J-Curve Effect Observable for Small North European Economies?
- 2003
-
Ingår i: Open Economies Review. - 0923-7992 .- 1573-708X. ; 14:2, s. 119-134
-
Tidskriftsartikel (refereegranskat)abstract
- The present study tests for the J-curve for five North European countries—Belgium, Denmark, The Netherlands, Norway, and Sweden—using generalized impulse response functions. The results provide empirical support for the J-curve. Each country has an impulse response function generated from a vector error-correction model that suggests that after a depreciation, there will be a dip in the export-import ratio within the first half-year after the depreciation. The long-run export-import ratio appears to be higher than the low point of this early dip in almost all cases. Also, in most cases, the export-import ratio appears in many periods after the depreciation to be converging from below to a higher long-run equilibrium.
|
|
| 19. |
- Hacker, R Scott
(författare)
-
Mobility and Regional Economic Downturns
- 2000
-
Ingår i: Journal of regional science. - : Wiley. - 0022-4146 .- 1467-9787. ; 40:1, s. 45-65
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper I show how higher unemployment in a region may reduce thepopulation's residential mobility within that region. A period of higher unemployment creates more uncertainty among individuals about future income and place of employment so those with significant moving costs are more likely to consider delaying a move. Periods of relatively higher unemployment may also be characterized by fewer new hirings and fewer job quits, both of which tend to dampen mobility. A multinomial logit analysis using Panel Study of Income Dynamics data is used to examine the effect of state unemployment rates on the decision to move.
|
|
| 20. |
- Hacker, R. Scott, 1964-, et al.
(författare)
-
Model selection in time series analysis : using information criteria as an alternative to hypothesis testing
- 2022
-
Ingår i: Journal of economic studies. - : Emerald Group Publishing Limited. - 0144-3585 .- 1758-7387. ; 49:6, s. 1055-1075
-
Tidskriftsartikel (refereegranskat)abstract
- Purpose: The issue of model selection in applied research is of vital importance. Since the true model in such research is not known, which model should be used from among various potential ones is an empirical question. There might exist several competitive models. A typical approach to dealing with this is classic hypothesis testing using an arbitrarily chosen significance level based on the underlying assumption that a true null hypothesis exists. In this paper, the authors investigate how successful the traditional hypothesis testing approach is in determining the correct model for different data generating processes using time series data. An alternative approach based on more formal model selection techniques using an information criterion or cross-validation is also investigated.Design/methodology/approach: Monte Carlo simulation experiments on various generating processes are used to look at the response surfaces resulting from hypothesis testing and response surfaces resulting from model selection based on minimizing an information criterion or the leave-one-out cross-validation prediction error.Findings: The authors find that the minimization of an information criterion can work well for model selection in a time series environment, often performing better than hypothesis-testing strategies. In such an environment, the use of an information criterion can help reduce the number of models for consideration, but the authors recommend the use of other methods also, including hypothesis testing, to determine the appropriateness of a model.Originality/value: This paper provides an alternative approach for selecting the best potential model among many for time series data. It demonstrates how minimizing an information criterion can be useful for model selection in a time-series environment in comparison to some standard hypothesis testing strategies.
|
|
| 21. |
- Hacker, R Scott, 1964-, et al.
(författare)
-
Optimal lag-length choice in stable and unstable VAR models under situations of homoscedasticity and ARCH
- 2008
-
Ingår i: Journal of Applied Statistics. - : Routledge. - 0266-4763 .- 1360-0532. ; 35:6, s. 601-615
-
Tidskriftsartikel (refereegranskat)abstract
- The performance of different information criteria - namely Akaike, corrected Akaike (AICC), Schwarz-Bayesian (SBC), and Hannan-Quinn - is investigated so as to choose the optimal lag length in stable and unstable vector autoregressive (VAR) models both when autoregressive conditional heteroscedasticity (ARCH) is present and when it is not. The investigation covers both large and small sample sizes. The Monte Carlo simulation results show that SBC has relatively better performance in lag-choice accuracy in many situations. It is also generally the least sensitive to ARCH regardless of stability or instability of the VAR model, especially in large sample sizes. These appealing properties of SBC make it the optimal criterion for choosing lag length in many situations, especially in the case of financial data, which are usually characterized by occasional periods of high volatility. SBC also has the best forecasting abilities in the majority of situations in which we vary sample size, stability, variance structure (ARCH or not), and forecast horizon (one period or five). frequently, AICC also has good lag-choosing and forecasting properties. However, when ARCH is present, the five-period forecast performance of all criteria in all situations worsens.
|
|
| 22. |
- Hacker, R. Scott, et al.
(författare)
-
Properties of Procedures Dealing with Uncertainty about Intercept and Deterministic Trend in Unit Root Testing
- 2014
-
Ingår i: Empirical Economics Review. - 2222-9736. ; 3:1, s. 83-97
-
Tidskriftsartikel (refereegranskat)abstract
- The classic Dickey-Fuller unit-root test can be applied using three different equations, depending upon the inclusion of a constant and/or a time trend in the regression equation. This paper investigates the size and power properties of a unit-root testing strategy outlined in Enders (2004), which allows for repeated testing of the unit root with the three equations depending on the significance of various parameters in the equations. This strategy is similar to strategies suggested by others for unit root testing. Our Monte Carlo simulation experiments show that serious mass significance problems prevail when using the strategy suggested by Enders. Excluding the possibility of unrealistic outcomes and using a priori information on whether there is a trend in the underlying time series, as suggested by Elder and Kennedy (2001), reduces the mass significance problem for the unit root test and improves power for that test. Subsequent testing for whether a trend exists is seriously affected by testing for the unit root first, however.
|
|
| 23. |
|
|
| 24. |
- Hacker, R Scott, et al.
(författare)
-
Tests for Causality between Integrated Variables Using Asymptotic and Bootstrap Distributions : Theory and Application
- 2006
-
Ingår i: Applied Economics. - : Informa UK Limited. - 0003-6846 .- 1466-4283. ; 38:13, s. 1489-1500
-
Tidskriftsartikel (refereegranskat)abstract
- Causality tests in the Granger's sense are increasingly applied in empirical research. Since the unit root revolution in time-series analysis, several modifications of tests for causality have been introduced in the literature. One of the recent developments is the Toda-Yamamoto modified Wald (MWALD) test, which is attractive due to its simple application, its absence of pre-testing distortions, and its basis on a standard asymptotical distribution irrespective of the number of unit roots and the cointegrating properties of the data. This study investigates the size properties of the MWALD test and finds that in small sample sizes this test performs poorly on those properties when using its asymptotical distribution, the chi-square. It is suggested that use be made of a leveraged bootstrap distribution to lower the size distortions. Monte Carlo simulation results show that an MWALD test based on a bootstrap distribution has much smaller size distortions than corresponding cases when the asymptotic distribution is used. These results hold for different sample sizes, integration orders, and error term processes (homoscedastic or ARCH). This new method is applied to the testing of the efficient market hypothesis
|
|
| 25. |
- Hacker, R Scott, et al.
(författare)
-
The Effect of Exchange Rate Changes on Trade Balances in the Short and Long Run : Evidence from German Trade with Transitional Central European Economies
- 2004
-
Ingår i: The Economics of Transition. - : Wiley. - 0967-0750 .- 1468-0351. ; 12:4, s. 777-799
-
Tidskriftsartikel (refereegranskat)abstract
- Using generalized impulse response functions, this study tests for the trade J-curve for three transitional central European countries – the Czech Republic, Hungary, and Poland – in their bilateral trade with respect to Germany. Our findings suggest that for each country there are some characteristics associated with a J-curve effect: after a (real or nominal) depreciation the export-to-import ratio briefly drops to below its initial value within a few months and then rises to a long run equilibrium value higher than the initial one.
|
|
