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"Schröder, Marc"
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Turkey as an energy hub? : contributions on Turkey's role in EU energy supply
Guaranteeing energy security is one of the most important challenges for Europe today. Especially since the crises in Ukraine, Europe's interest in an additional supply line of gas and oil to Europe through Turkey has been growing steadily. In both political and academic discourse the question of whether Turkey can develop into a possible future 'energy hub' is a hotly debated issue. The country's geographical position is a big advantage as more than 70 per cent of the world's oil and gas reserves are located close by. The country may thus hold a key position in the distribution of oil and gas. Will Turkey, itself almost fully dependent on imports, be capable of becoming an energy hub? This edited volume examines Turkey's prospects as a possible energy hub and in its role in the EU's energy security. The contributions it contains reflect geopolitical dynamics and interests, economic trends, and the prevailing perceptions of this issue in Turkey and the European Union.-- Provided by Publisher.
BOOK
Calculation of the minimum clinically important difference (MCID) using different methodologies: case study and practical guide
Introduction
Establishing thresholds of change that are actually meaningful for the patient in an outcome measurement instrument is paramount. This concept is called the minimum clinically important difference (MCID). We summarize available MCID calculation methods relevant to spine surgery, and outline key considerations, followed by a step-by-step working example of how MCID can be calculated, using publicly available data, to enable the readers to follow the calculations themselves.
Methods
Thirteen MCID calculations methods were summarized, including anchor-based methods, distribution-based methods, Reliable Change Index, 30% Reduction from Baseline, Social Comparison Approach and the Delphi method. All methods, except the latter two, were used to calculate MCID for improvement of Zurich Claudication Questionnaire (ZCQ) Symptom Severity of patients with lumbar spinal stenosis. Numeric Rating Scale for Leg Pain and Japanese Orthopaedic Association Back Pain Evaluation Questionnaire Walking Ability domain were used as anchors.
Results
The MCID for improvement of ZCQ Symptom Severity ranged from 0.8 to 5.1. On average, distribution-based methods yielded lower MCID values, than anchor-based methods. The percentage of patients who achieved the calculated MCID threshold ranged from 9.5% to 61.9%.
Conclusions
MCID calculations are encouraged in spinal research to evaluate treatment success. Anchor-based methods, relying on scales assessing patient preferences, continue to be the “gold-standard” with receiver operating characteristic curve approach being optimal. In their absence, the minimum detectable change approach is acceptable. The provided explanation and step-by-step example of MCID calculations with statistical code and publicly available data can act as guidance in planning future MCID calculation studies.
Journal Article
Association of age with incidence and timing of recurrence after microdiscectomy for lumbar disc herniation
ObjectiveRecurrent lumbar disc herniation (LDH) is the most frequent reason for reoperation after lumbar microdiscectomy. While several risk factors for recurrent LDH have been well-described, the effect of age on recurrence remains unclear, especially concerning the timing of recurrent LDH.MethodsFrom a prospective registry, we identified all patients who underwent tubular microdiscectomy for LDH. Recurrent LDH was defined as reoperation for LDH at the same index level and side. The associations among age and incidence of recurrent LDH as well as on time to recurrent LDH were statistically evaluated using multivariable analysis of covariance, linear regression, and Cox proportional hazards modelling.ResultsOf the 3013 patients who underwent surgery for LDH, 166 (5.5%) had to undergo reoperation due to LDH recurrence. Uni- and multivariable analysis revealed no influence of age on the incidence of recurrent LDH (both p > 0.05). Linear regression indicated earlier reoperation in older patients, both with (β = −0.248) and without (β = −0.374) correction for confounders (both p < 0.05). An additional survival analysis found that patients aged over 35 years had recurrent LDH significantly earlier (hazard ratio 0.617, p = 0.013).ConclusionIn an analysis of a large prospective database of patients undergoing microdiscectomy for lumbar disc herniation, we found that younger patients do not have a higher reoperation probability than their older counterparts, even after correcting for multiple confounders. However, older patients tend to experience recurrent LDH significantly earlier after the index surgery compared to younger patients.
Journal Article
Gender differences in degenerative spine surgery: Do female patients really fare worse?
PurposePrior data has set the precedent that female patients fare somewhat worse than men after spine surgery. We aimed to evaluate the effect of gender on patient-reported outcomes after lumbar spine surgery for degenerative pathologies.MethodsWe identified a consecutive cohort of patients from a prospective registry. Absolute values, as well as change scores for back and leg pain severity (numeric rating scale [NRS]), functional disability (Oswestry disability index [ODI]), and health-related quality of life (HRQOL) as assessed by EQ-5D were compared among male and female patients.ResultsOf the 3279 included patients, 1543 (47%) were female. At baseline, women reported higher NRS for back and leg pain, higher ODI, but equal HRQOL (all p < 0.05). Otherwise, both groups had comparable baseline data. The absolute differences in patient-reported outcomes persisted at the 6-week, 12- and 24-months follow-up, with women now additionally reporting worse HRQOL as assessed by EQ-5D (all p < 0.05). For all outcome measures, change scores were equal among male and female patients, as were the incidences of complications and reoperations (all p > 0.05). Clinical success was achieved in 82% of men and 79% of women (p = 0.34).ConclusionsFemale patients are generally scheduled for surgery with a more advanced disease state. While women seem to report more severe symptoms at long-term follow-up, the degree of improvement is equal among men and women. Female patients may thus fare worse in terms of absolute scores, but enjoy the same benefit from surgery in relative terms.Graphical abstractThese slides can be retrieved under Electronic Supplementary Material.
Journal Article
Can objective functional impairment in lumbar degenerative disease be reliably assessed at home using the five-repetition sit-to-stand test? A prospective study
PurposeObjective functional tests like the five-repetition sit-to-stand test (5R-STS) can supplement an objective dimension to conventional patient-reported outcome measures. The reliability of unsupervised obtainment of 5R-STS performance is currently unknown.MethodsWe included patients with degenerative pathologies of the lumbar spine. Patients performed the 5R-STS during the initial clinical visit (supervised), as well as at home after instruction by a physiotherapist. At home, patients were first timed by a relative (unsupervised) and subsequently produced a video recording of themselves performing the 5R-STS for digital measurement (telesupervised). Two raters independently assessed the recordings.ResultsOne hundred and twenty-one patients were recruited, of which 100 were eligible. Eighty-eight reported unsupervised results. Sixty-four returned recordings, of which 61 were ratable. Both unsupervised (r: 0.94, 95% CI 0.91–0.96, p < 0.001) and telesupervised (r: 0.90, 95% CI 0.83–0.94, p < 0.001) measurements demonstrated excellent correlation with clinical test times. Patients did not perform more slowly at home (p > 0.05). The interrater agreement for digital judgement of the telesupervised recording was excellent (ICC: 0.996, 95% CI 0.993–0.998, p < 0.001). We confirmed convergent validity with self-reported disability, back pain, and quality of life (all p < 0.05), but not with leg pain (p = 0.189).ConclusionsUnsupervised at-home assessment using the 5R-STS is highly reliable. There does not appear to be a specific need for patients to return for a supervised 5R-STS follow-up. Rather, instructions can be provided, and the test performed and rated by a partner or family member at home. This is logistically and economically advantageous for patients, clinicians, and researchers.Trial registry numberClinicalTrials.gov Identifier: NCT03321357.Graphical abstractThese slides can be retrieved under Electronic Supplementary Material.
Journal Article
Overweight and smoking promote recurrent lumbar disk herniation after discectomy
PurposeRecurrent lumbar disk herniation (rLDH) following lumbar microdiscectomy is common. While several risk factors for primary LDH have been described, risk factors for rLDH have only sparsely been investigated. We evaluate the effect of Body mass index (BMI) and smoking on the incidence and timing of rLDH.MethodsFrom a prospective registry, we identified all patients undergoing primary tubular microdiscectomy (tMD), with complete BMI and smoking data, and a minimum 12-month follow-up. We defined rLDH as reherniation at the same level and side requiring surgery. Overweight was defined as BMI > 25, and obesity as BMI > 30. Intergroup comparisons and age- and gender-adjusted multivariable regression were carried out. We conducted a survival analysis to assess the influence of BMI and smoking on time to reoperation.ResultsOf 3012 patients, 166 (5.5%) underwent re-microdiscectomy for rLDH. Smokers were reoperated more frequently (6.4% vs. 4.0%, p = 0.007). Similarly, rLDH was more frequent in obese (7.5%) and overweight (5.9%) than in normal-weight patients (3.3%, p = 0.017). Overweight smokers had the highest rLDH rate (7.6%). This effect of smoking (Odds ratio: 1.63, 96% CI: 1.12–2.36, p = 0.010) and BMI (Odds ratio: 1.09, 95% CI: 1.02–1.17, p = 0.010) persisted after controlling for age and gender. Survival analysis demonstrated that rLDH did not occur earlier in overweight patients and/or smokers.ConclusionsBMI and smoking may directly contribute to a higher risk of rLDH, but do not accelerate rLDH development. Smoking cessation and weight loss in overweight or obese patients ought to be recommended with discectomy to reduce the risk for rLDH.
Journal Article
Dynamic Atomic Congestion Games with Seasonal Flows
We propose a model of discrete time dynamic congestion games with atomic players and a single source-destination pair. The latencies of edges are composed of free-flow transit times and possible queuing time due to capacity constraints. We give a precise description of the dynamics induced by the individual strategies of players and of the corresponding costs, either when the traffic is controlled by a planner, or when players act selfishly. In parallel networks, optimal and equilibrium behavior eventually coincide, but the selfish behavior of the initial players has consequences that cannot be undone and are paid by all future generations. In more general topologies, our main contributions are threefold. First, we illustrate a new dynamic version of Braess paradox: the presence of initial queues in the network may decrease the long-run costs in equilibrium. This paradox can arise in networks for which no Braess paradox was previously known. Second, we show that equilibria are not unique and can induce very different long-run costs. In particular, we give a sequence of networks such that the price of stability is equal to 1, and the price of anarchy is equal to
n
− 1, where
n
is the number of vertices. Third, we propose an extension to model seasonalities by assuming that departure flows fluctuate periodically over time. We introduce a measure that captures the queues induced by periodicity of inflows. For optimal and equilibrium flows in parallel networks this measure is the increase in cost compared to uniform departures.
The electronic companion is available at
https://doi.org/10.1287/opre.2017.1683
.
Journal Article
Initial classification of low back and leg pain based on objective functional testing: a pilot study of machine learning applied to diagnostics
ObjectiveThe five-repetition sit-to-stand (5R-STS) test was designed to capture objective functional impairment and thus provided an adjunctive dimension in patient assessment. The clinical interpretability and confounders of the 5R-STS remain poorly understood. In clinical use, it became apparent that 5R-STS performance may differ between patients with lumbar disk herniation (LDH), lumbar spinal stenosis (LSS) with or without low-grade spondylolisthesis, and chronic low back pain (CLBP). We seek to evaluate the extent of diagnostic information contained within 5R-STS testing.MethodsPatients were classified into gold standard diagnostic categories based on history, physical examination, and imaging. Crude and adjusted comparisons of 5R-STS performance were carried out among the three diagnostic categories. Subsequently, a machine learning algorithm was trained to classify patients into the three categories using only 5R-STS test time and patient age, gender, height, and weight.ResultsFrom two prospective studies, 262 patients were included. Significant differences in crude and adjusted test times were observed among the three diagnostic categories. At internal validation, classification accuracy was 96.2% (95% CI 87.099.5%). Classification sensitivity was 95.7%, 100%, and 100% for LDH, LSS, and CLBP, respectively. Similarly, classification specificity was 100%, 95.7%, and 100% for the three diagnostic categories.Conclusion5R-STS performance differs according to the etiology of back and leg pain, even after adjustment for demographic covariates. In combination with machine learning algorithms, OFI can be used to infer the etiology of spinal back and leg pain with accuracy comparable to other diagnostic tests used in clinical examination.Graphic abstractThese slides can be retrieved under Electronic Supplementary Material.
Journal Article
Identifying clusters of objective functional impairment in patients with degenerative lumbar spinal disease using unsupervised learning
Objectives
The five-repetition sit-to-stand (5R-STS) test was designed to capture objective functional impairment (OFI), and thus provides an adjunctive dimension in patient assessment. It is conceivable that there are different subsets of patients with OFI and degenerative lumbar disease. We aim to identify clusters of objectively functionally impaired individuals based on 5R-STS and unsupervised machine learning (ML).
Methods
Data from two prospective cohort studies on patients with surgery for degenerative lumbar disease and 5R-STS times of ≥ 10.5 s—indicating presence of OFI.
K
-means clustering—an unsupervised ML algorithm—was applied to identify clusters of OFI. Cluster hallmarks were then identified using descriptive and inferential statistical analyses.
Results
We included 173 patients (mean age [standard deviation]: 46.7 [12.7] years, 45% male) and identified three types of OFI. OFI Type 1 (57 pts., 32.9%), Type 2 (81 pts., 46.8%), and Type 3 (35 pts., 20.2%) exhibited mean 5R-STS test times of 14.0 (3.2), 14.5 (3.3), and 27.1 (4.4) seconds, respectively. The grades of OFI according to the validated baseline severity stratification of the 5R-STS increased significantly with each OFI type, as did extreme anxiety and depression symptoms, issues with mobility and daily activities. Types 1 and 2 are characterized by mild to moderate OFI—with female gender, lower body mass index, and less smokers as Type I hallmarks.
Conclusions
Unsupervised learning techniques identified three distinct clusters of patients with OFI that may represent a more holistic clinical classification of patients with OFI than test-time stratifications alone, by accounting for individual patient characteristics.
Journal Article
Predictive value of the five-repetition sit-to-stand test for outcomes after surgery for lumbar disc herniation: prospective study
Objective
It is unknown whether presence of pre-operative objective functional impairment (OFI) can predict post-operative outcomes in patients with lumbar disc herniation (LDH). We aimed to determine whether pre-operative OFI measured by the five-repetition sit-to-stand test (5R-STS) could predict outcomes at 12-months post-discectomy.
Methods
Adult patients with LDH scheduled for surgery were prospectively recruited from a Dutch short-stay spinal clinic. The 5R-STS time and patient reported outcome measures (PROMs) including Oswestry Disability Index, Roland-Morris Disability Questionnaire, Visual Analogue Scale (VAS) for back and leg pain, EQ-5D-3L health-related quality of life, EQ5D-VAS and ability to work were recorded pre-operatively and at 12-months. A 5R-STS time cut-off of ≥ 10.5 s was used to determine OFI. Mann–Whitney and Chi-square tests were employed to determine significant differences in post-operative outcomes between groups stratified by presence of pre-operative OFI.
Results
We recruited 134 patients in a prospective study. Twelve-month follow-up was completed by 103 (76.8%) patients. Mean age was 53.2 ± 14.35 years and 50 (48.5%) patients were female. Pre-operatively, 53 (51.5%) patients had OFI and 50 (48.5%) did not. Post-operatively, patients with OFI experienced a significantly greater mean change (
p
< 0.001) across all PROMs compared to patients without OFI, except leg pain (
p
= 0.176). There were no significant differences in absolute PROMs between groups at 12-months (all
p
> 0.05).
Conclusions
The presence of OFI based on 5R-STS time does not appear to decrease a patient’s likelihood of experiencing satisfactory post-operative outcomes. The 5R-STS cannot predict how a patient with LDH will respond to surgery at 12-month follow-up.
Journal Article