| 1. |
|
|
| 2. |
|
|
| 3. |
- Moberg, Christina, et al.
(författare)
-
De unga gör helt rätt när de stämmer staten
- 2022
-
Ingår i: Aftonbladet. - 1103-9000.
-
Tidskriftsartikel (populärvet., debatt m.m.)abstract
- 1 620 forskare och lärare i forskarvärlden: Vi ställer oss bakom Auroras klimatkrav
|
|
| 4. |
|
|
| 5. |
|
|
| 6. |
- Ekström, Hanna, et al.
(författare)
-
Barking up the wrong tree? : A guide to forest owner typology methods
- 2024
-
Ingår i: Forest Policy and Economics. - : Elsevier. - 1389-9341 .- 1872-7050. ; 163
-
Tidskriftsartikel (refereegranskat)abstract
- Creating typologies of forest owners is a common approach for analyzing and understanding heterogeneity in responses to forest policies and management practice uptake. While many forest owner typologies have been developed, only a few quantitative methods dominate the field with little information on how methodological choice affects outcomes. In this study we compare five methods for quantitative typology formation and ask what type of information each method provides, and to which degree the methods complement each other. Empirically we use data from a survey conducted in 2014–2015 about Swedish forest owner's objectives, attitudes, and factors of decision-making. The results show that individual forest owners are assigned to different clusters by the compared methods, and how each method highlights different aspects of forest owner characteristics. The study shows the importance of method selection as it influences how we can describe and interpret forest owners in connection to policy adoption, uptake of practices, and environmental awareness. We conclude by providing basis for a methodological guidance on how to make judgments when selecting method(s) to typology formation based on research purpose and approach.
|
|
| 7. |
- Ekström, Hanna, et al.
(författare)
-
Barking up the wrong tree? : A guide to forest owner typology methods
- 2024
-
Ingår i: Forest Policy and Economics. - 1389-9341. ; 163
-
Tidskriftsartikel (refereegranskat)abstract
- Creating typologies of forest owners is a common approach for analyzing and understanding heterogeneity in responses to forest policies and management practice uptake. While many forest owner typologies have been developed, only a few quantitative methods dominate the field with little information on how methodological choice affects outcomes. In this study we compare five methods for quantitative typology formation and ask what type of information each method provides, and to which degree the methods complement each other. Empirically we use data from a survey conducted in 2014–2015 about Swedish forest owner's objectives, attitudes, and factors of decision-making. The results show that individual forest owners are assigned to different clusters by the compared methods, and how each method highlights different aspects of forest owner characteristics. The study shows the importance of method selection as it influences how we can describe and interpret forest owners in connection to policy adoption, uptake of practices, and environmental awareness. We conclude by providing basis for a methodological guidance on how to make judgments when selecting method(s) to typology formation based on research purpose and approach.
|
|
| 8. |
- Ekström, Hanna, et al.
(författare)
-
Modelling forests as social-ecological systems : A systematic comparison of agent-based approaches
- 2024
-
Ingår i: Environmental Modelling and Software. - 1364-8152 .- 1873-6726. ; 175
-
Forskningsöversikt (refereegranskat)abstract
- The multifunctionality of forest systems calls for appropriately complex modelling approaches to capture social and ecosystem dynamics. Using a social-ecological systems framework, we review the functionality of 31 existing agent-based models applied to managed forests. Several applications include advanced cognitive and emotional decision-making, crucial for understanding complex sustainability challenges. However, far from all demonstrate representation of key elements in a social-ecological system like direct interactions, and dynamic representations of social and ecological processes. We conclude that agent-based approaches are adequately complex for simulating both social and ecological subsystems, but highlight three main avenues for further development: i) robust methodological standards for calibration and validation of agent-based approaches; ii) modelling of agent learning, adaptive governance and feedback loops; iii) coupling to ecological models such as dynamic vegetation models or species distribution models. We round-off by providing a set of questions to support social-ecological systems modelling choices.
|
|
| 9. |
- Ekström, Joakim, 1980-, et al.
(författare)
-
Simulation based optimisation of toll levels in urban road traffic networks
- 2014
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- There has recently been a growing interest in analysing road pricing schemes in urban areas using dynamic traffic assignment (DTA) tools. The motivation behind this development is the problem for static transportation models to accurately predict travel time savings, from introducing road pricing, in networks with severe congestion. Finding optimal toll levels and locations in urban road traffic networks has so far mainly been studied using either derivative-free heuristics (e.g. genetic algorithms and simulated annealing) or ascent methods. Both approaches rely on fast computations of the road users response (traffic flows, travel times and demands), given the road pricing scheme, and for the case of ascent methods, the methods also rely on fast computations (or rather approximation) of derivatives. Using DTA tools for evaluating the road users’ response to a pricing scheme is, however, very computationally expensive. Previously developed methods are therefore not suitable to use together with DTA.Surrogate models, e.g. in terms of response surfaces, are commonly used for optimisation problems with expensive-to-evaluate objective functions. The surrogate model is used for approximating the expensive-to-evaluate objective function, and the optimisation is then done on the surrogate model instead. The performances of optimisation methods based on surrogate models are, however, dependent on experimental design, infill strategy and choice of surrogate model itself. The experimental design will give the initial set of toll levels, for which the DTA needs to be evaluated, the infill strategy determined additional toll levels to be evaluated by the DTA, and the choice of surrogate model will give the functional form to be fitted to the sampled toll levels.We apply a surrogate model framework for optimising toll levels in a multiple cordon pricing scheme. In the first stage we evaluate the experimental design, infill strategy and choice of surrogate model, using a static macroscopic traffic model. This allows a large number of experiments to be carried out, which would not be possible with a DTA tool. It also allows us to compare the performance of the surrogate modelling approach with other global optimisation methods. In the second stage, the insight which has been gained from the experiments with the static model is used when applying the surrogate modelling approach to a DTA model of Stockholm.Computational results are presented for a Stockholm network with three cordons, each with differentiated toll level in both directions, resulting in a total of six toll level variables. Surrogate models in the form of Radial Basis Functions and Kriging models are evaluated with a static model of Stockholm, for different initial experimental designs, infill strategies and choice of surrogate models. In comparison with previously developed derivative based methods for static models, our results show that the surrogate based optimisation approach performs better, since it allows for metaheuristic methods to search for global optimal solutions efficiently.
|
|
| 10. |
- Ekström, Joakim, 1980-, et al.
(författare)
-
Surrogatbaserad optimering av avgiftsnivåer i trängselavgiftssystem
- 2015
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Trängselskatt finns idag i både Stockholm och Göteborg, och det är troligt att utformningen av dessa trängselskattesystem kommer att justeras framöver med avseende på avgiftsnivå, placering och tidpunkt. För Stockholm finns beslut om ändring från januari 2016 och i Göteborg ändrades avgiftsnivåerna i januari 2015. I detta projekt utvecklas metoder som ska kunna ge stöd vid justering av avigiftsnivåer, så att en så stor samhällsekonomisk nytta som är möjligt uppnås med trängselskattesystemet.För storstadsområden, där det under rusningstrafik är trängsel i delar av nätverket, är trängselskatt främst intressant att analysera med dynamiska transportmodeller. Tidigare utveckling av metoder för optimal avgiftssättning har dock främst fokuserat på statiska modeller, exempelvis Emme, som har kända problem med att korrekt uppskatta förändring i restider när det är trängsel i delar av trafiknätverket. I detta projekt har vi därför tillämpat surrogat-baserad optimering, som är en metodansats som ställer få krav på vilken transportmodell som används. Den dynamiska transportmodellen Regent/VisumDUE finns sedan tidigare implementerad för Stockholmsregionen, och har därför även använts i detta projekt. VisumDUE är en makroskopisk nätutläggningsmodell med dynamiskt ruttval, och Regent är en efterfrågemodell som innehåller resgenerering, färdmedelsval och destinationsval för arbetsresor[1].Surrogat-baserad optimering erbjuder ett ramverk för optimering av problem med beräkningsmässigt kostsamma målfunktioner. Genom att approximera en funktionsyta till samplade punkter från den kostsamma målfunktionen, kan optimeringen istället göras över den approximerade funktionsytan. För Regent/VisumDUE tar utvärderingen av ett givet trängselskattescenario ca tio timmar, och det är denna beräkningstid som gör målfunktionen kostsam. Givet ett antal samplade punkter, görs ytterligare sampling utifrån en given strategi för att förbättra approximationen, så kallad iterativ sampling. Inom ramverket finns dock en mängd möjligheter för hur de olika komponenterna designas. Därför är det svårt att utvärdera surrogat-baserad optimering med endast Regent/VisumDUE. En statisk transportmodell har därför använts för att utvärdera ett antal kombinationer av samplingsstrategi och funktionsyta. Den mest lovande kombinationen har sedan även utvärderats med Regent/VisumDUE. För att vara praktiskt tillämpbart i framtiden har fokus i projektet varit att utvärdera hur metodansatsen fungerar när antalet möjliga tulluppsättningar är kraftigt begränsat (20-40 stycken).Det scenario som har använts som grund i projektet är trängselskatt i Stockholm på nuvarande tullring, på Essingeleden samt på innerstadsbroarna. Skatten är differentierad med avseende på riktning, vilket ger sex olika skattenivåer att optimera. Optimeringen har gjorts för trängselskattenivå under maxtimmen. I det dynamiska fallet har trängselskattens nivå utanför maxtimme funnits med som indata, men samma tidsprofil som på nuvarande tullring har antagits i alla scenarier (avgiftstrappa 50%, 75%, 100%, 75%, 50%). Utvärderingen med den statiska transportmodellen visar att lösningar nära globalt optimum kan uppnås med endast 40 utvärderade trängselskattenivåer, och en tydlig förbättring av den samhällsekonomiska nyttan uppnås redan vid 20 utvärderade trängselskattenivåer.Även med ett kraftigt begränsat antal utvärderingar av den kostsamma målfunktionen i Regent/VisumDUE, har vi visat att det är möjligt att använda metodansatsen. En tydlig förbättring av den samhällsekonomiska nyttan uppnås med endast 22 utvärderade trängselskattenivåer. Ytterligare experiment skulle dock behövas för att undersöka hur stor denna förbättring är i förhållande till vad som skulle kunna uppnås.
|
|
| 11. |
- Ekström, Joakim, 1980-, et al.
(författare)
-
Surrogate-based optimisation of toll levels in congestion pricing schemes
- 2014
-
Ingår i: Transportation Infrastructure. - Hong Kong : Hong Kong Society of Transportation Studies Limited. - 9789881581433 ; , s. 209-216
-
Konferensbidrag (refereegranskat)abstract
- There has recently been a growing interest in analysing road pricing schemes in urban areas using dynamic traffic assignment (DTA) tools. Finding optimal toll levels in cordon based road pricing schemes has so far mainly been studied using either derivative-free heuristics or ascent methods. For future use of DTA tools such methods are not suitable and in this paper we investigate how a surrogate modelling framework can be used instead. We focus on cases when the number of costly objective function evaluations is limited to between 20 and 40. In order to allow a large number of different configurations of the surrogate modelling framework to be evaluated, a static user equilibrium model is used for simulating the road users’ response to a given pricing scheme. The results show that for a realistic scenario, valuable information on close to optimal toll levels can be achieved with only 20 costly function evaluations.
|
|
| 12. |
- Ekström, Joakim, et al.
(författare)
-
Surrogate-based optimization of cordon toll levels in congested traffic networks
- 2016
-
Ingår i: Journal of Advanced Transportation. - : John Wiley & Sons. - 0197-6729 .- 2042-3195. ; 50:6, s. 1008-1033
-
Tidskriftsartikel (refereegranskat)abstract
- The benefit, in terms of social surplus, from introducing congestion charging schemes in urban networks is depending on the design of the charging scheme. The literature on optimal design of congestion pricing schemes is to a large extent based on static traffic assignment, which is known for its deficiency in correctly predict travel times in networks with severe congestion. Dynamic traffic assignment can better predict travel times in a road network, but are more computational expensive. Thus, previously developed methods for the static case cannot be applied straightforward. Surrogate-based optimization is commonly used for optimization problems with expensive-to-evaluate objective functions. In this paper, we evaluate the performance of a surrogate-based optimization method, when the number of pricing schemes, which we can afford to evaluate (because of the computational time), are limited to between 20 and 40. A static traffic assignment model of Stockholm is used for evaluating a large number of different configurations of the surrogate-based optimization method. Final evaluation is performed with the dynamic traffic assignment tool VisumDUE, coupled with the demand model Regent, for a Stockholm network including 1240 demand zones and 17 000 links. Our results show that the surrogate-based optimization method can indeed be used for designing a congestion charging scheme, which return a high social surplus.
|
|
| 13. |
- Ekström, Nils, et al.
(författare)
-
Aspirin treatment and risk of first incident cardiovascular diseases in patients with type 2 diabetes : an observational study from the Swedish National Diabetes Register
- 2013
-
Ingår i: BMJ Open. - : BMJ Publishing Group. - 2044-6055. ; 3:4, s. e002688-
-
Tidskriftsartikel (refereegranskat)abstract
- Objectives To investigate the benefits and risks associated with aspirin treatment in patients with type 2 diabetes and no previous cardiovascular disease (CVD) in clinical practice. Design Population-based cohort study between 2005 and 2009, mean follow-up 3.9years. Setting Hospital outpatient clinics and primary care in Sweden. Participants Men and women with type 2 diabetes, free from CVD, including atrial fibrillation and congestive heart failure, at baseline, registered in the Swedish National Diabetes Register, with continuous low-dose aspirin treatment (n=4608) or no aspirin treatment (n=14038). Main outcome measures Risks of CVD, coronary heart disease (CHD), stroke, mortality and bleedings, associated with aspirin compared with no aspirin, were analysed in all patients and in subgroups by gender and estimated cardiovascular risk. Propensity scores were used to adjust for several baseline risk factors and characteristics at Cox regression, and the effect of unknown covariates was evaluated in a sensitivity analysis. Results There was no association between aspirin use and beneficial effects on risks of CVD or death. Rather, there was an increased risk of non-fatal/fatal CHD associated with aspirin; HR 1.19 (95% CI 1.01 to 1.41), p=0.04. The increased risk of cardiovascular outcomes associated with aspirin was seen when analysing women separately; HR 1.41 (95% CI 1.07 to 1.87), p=0.02, and HR 1.28 (95% CI 1.01 to 1.61), p=0.04, for CHD and CVD, respectively, but not for men separately. There was a trend towards increased risk of a composite of bleedings associated with aspirin, n=157; HR 1.41 (95% CI 0.99 to 1.99). Conclusions The results support the trend towards more restrictive use of aspirin in patients with type 2 diabetes and no previous CVD. More research is needed to explore the differences in aspirin's effects in women and men.
|
|
| 14. |
- Ekström, Nils, et al.
(författare)
-
Cardiovascular safety of glucose-lowering agents as add-on medication to metformin treatment in type 2 diabetes: report from the Swedish National Diabetes Register
- 2016
-
Ingår i: Diabetes Obesity & Metabolism. - : Wiley. - 1462-8902 .- 1463-1326. ; 18:10, s. 990-998
-
Tidskriftsartikel (refereegranskat)abstract
- Aim: To investigate the relative safety of various glucose-lowering agents as add-on medication to metformin in type 2 diabetes in an observational study linking five national health registers. Research design and methods: Patients with type 2 diabetes who had been on metformin monotherapy and started another agent in addition to metformin were eligible for inclusion. The study period was 2005-2012. Adjusted hazard ratios (HRs) with 95% confidence intervals (CIs) of mortality, cardiovascular disease (CVD), coronary heart disease (CHD), stroke and congestive heart failure (CHF) were estimated using Cox proportional hazards models, weighted for a propensity score. Results: Of the 20 422 patients included in the study, 43% started on second-line treatment with sulphonylurea (SU), 21% basal insulin, 12% thiazolidinedione (TZD), 11% meglitinide, 10% dipeptidyl peptidase-4 (DPP-4) inhibitor, 1% glucagon-like peptide-1 (GLP-1) receptor agonist and 1% acarbose. At the index date, the mean patient age was similar to 60 years for all groups except the GLP-1 receptor agonist (56.0 years) and SU (62.9 years) groups. Diabetes duration and glycated haemoglobin levels were similar in all groups. When compared with SU, basal insulin was associated with an 18% higher risk and TZD with a 24% lower risk of mortality [HR 1.18 (95% CI 1.03-1.36) and 0.76 (95% CI 0.62-0.94)], respectively. DPP-4 inhibitor treatment was associated with significantly lower risks of CVD, fatal CVD, CHD, fatal CHD and CHF. Conclusions: This nationwide observational study showed that second-line treatment with TZD and DPP-4 inhibitor as add-on medication to metformin were associated with significantly lower risks of mortality and cardiovascular events compared with SU, whereas basal insulin was associated with a higher risk of mortality.
|
|
| 15. |
|
|
| 16. |
|
|
| 17. |
|
|
| 18. |
- Ekström, Nils, et al.
(författare)
-
Glucose-lowering treatment and clinical results in 163 121 patients with type 2 diabetes: an observational study from the Swedish national diabetes register
- 2012
-
Ingår i: Diabetes Obesity & Metabolism. - : Wiley. - 1462-8902 .- 1463-1326. ; 14:8, s. 717-726
-
Tidskriftsartikel (refereegranskat)abstract
- Aims: To analyse clinical characteristics and treatment results in unselected type 2 diabetes mellitus (T2DM) patients, with non-pharmacological treatment as well as the most commonly used pharmacological glucose-lowering treatment regimens, in everyday clinical practice. Methods: In this population-based cross-sectional study, information was linked from the Swedish National Diabetes Register, Prescribed Drug Register and Patient Register. T2DM patients with non-pharmacological treatment and T2DM patients continuously using the 12 most common pharmacological treatment regimens were included in the study (n = 163121). Results: There were statistically significant differences in clinical characteristics between the groups. Patients with insulin-based treatment regimens had the longest duration of diabetes and more cardiovascular risk factors than the T2DM-population in general. The proportion of patients reaching HbA1c =7% varied between 70.1% (metformin) and 25.0% [premixed insulin (PMI) + SU) in patients with pharmacological treatment. 84.8% of the patients with non-pharmacological treatment reached target. Compared to patients on metformin, patients on other pharmacological treatments had a lower likelihood, with hazard ratios ranging from 0.58; 95% confidence interval (CI), 0.540.63 to 0.97;0.940.99, of having HbA1c =7% (adjusted for covariates). Patients on insulin-based treatments had the lowest likelihood, while non-pharmacological treatment was associated with an increased likelihood of having HbA1c =7%. Conclusion: This nation-wide study shows insufficiently reached treatment goals for haemoglobin A1c (HbA1c) in all treatment groups. Patients on insulin-based treatment regimens had the longest duration of diabetes, more cardiovascular risk factors and the highest proportions of patients not reaching HbA1c target.
|
|
| 19. |
|
|
| 20. |
|
|
| 21. |
|
|
| 22. |
|
|
| 23. |
|
|
| 24. |
|
|
| 25. |
|
|
