Jacob Pedersen

Simulated annealing with constant thermodynamic speed

Abstract Arguments are presented to the effect that the optimal annealing schedule for simulated annealing proceeds with constant thermodynamic speed, i.e., with d T d t = -(vT) (ϵ C ) , where T is the temperature, ϵ is the relaxation time, C is the heat capacity, t is the time, and v is the (constant) thermodynamic speed. Experimental results on a graph partitioning problem which can be solved exactly are shown to be consistent with this conjecture.

Transitions between Sickness Absence, Work, Unemployment, and Disability in Denmark 2004-2008

OBJECTIVES Studies of labor market outcomes like sickness absence are usually restricted to a single outcome. This paper investigates the use of multi-state models for studying multiple transitions between sick-listing, work, unemployment, and disability pension by analyzing longitudinal register data. Every person sick-listed in Denmark during 2004 was followed until the spring of 2008. METHODS A multi-state model was used to analyze transitions between four states: work, sickness absence, unemployment, and disability pension. The first three are possible recurrent states. The predictor variables include age group, gender, geographical region, chronic disease, temporary disease, self-employment sickness absence insurance, and pregnancy. The relative effects of previous transitions were also studied. RESULTS Risk of transition from sickness absence to disability pension differs with age and geographical region. Those aged 20-29 years have an increased risk of transitioning from work to sickness absence and from sickness absence to unemployment. The self-employed have increased risk of transitioning from work to sickness absence. Those with chronic disease have increased risk of sickness absence, but also a greater probability of returning to work. Previous sickness absence increases the risk of transitioning from work to sickness absence, from sickness absence to unemployment, from work to unemployment, and from work to disability pension. CONCLUSIONS The multi-state model is an effective way of analyzing register data and the transitions between sickness absence, work, unemployment, and disability pension. These methods can be used to develop better predictive models of sickness absence, return to work, unemployment, and disability.

The transition between work, sickness absence and pension in a cohort of Danish colorectal cancer survivors

Objectives The aim of this study was to evaluate the impact of socioeconomic and clinical factors on the transitions between work, sickness absence and retirement in a cohort of Danish colorectal cancer survivors. Design Register-based cohort study with up to 10 years of follow-up. Setting Population-based study with use of administrative health-related and socioeconomic registers. Participants All persons (N=4343) diagnosed with colorectal cancer in Denmark during the years 2001–2009 while they were in their working age (18–63 years) and who were part of the labour force 1 year postdiagnosis. Primary and secondary outcome measures By the use of multistate models in Cox proportional hazards models, we analysed the HR for re-employment, sickness absence and retirement in models including clinical as well as health-related variables. Results 1 year after diagnosis, 62% were working and 58% continued until the end of follow-up. Socioeconomic factors were found to be associated with retirement but not with sickness absence and return to work. The risk for transition from work to sickness absence increased if the disease was diagnosed at a later stage (stage III) 1.52 (95% CI 1.21 to 1.91), not operated curatively 1.35 (95% CI 1.11 to 1.63) and with occurrence of postoperative complications 1.25 (95% CI 1.11 to 1.41). The opposite was found for the transition from sickness absence back to work. Conclusions This nationwide study of colorectal cancer patients who have survived 1 year shows that the stage of disease, general health condition of the individual, postoperative complications and the history of sickness absence and unemployment have an impact on the transition between work, sickness absence and disability pension. This leads to an increased focus on the rehabilitation process for the more vulnerable persons who have a combination of severe disease and a history of work-related problems with episodes outside the working market.

Optimal ensemble size for parallel implementations of simulated annealing

Abstract We determine the optimal ensemble size for a simulated annealing problem based on assumptions about scaling properties of the system dynamics and of the density of states in the low energy regime. The derivations indicate the optimal annealing time for any one ensemble member, thereby providing a stopping criterion and an explanation for the “brick wall effect”.

Effect of Rheumatoid Arthritis on Longterm Sickness Absence in 1994-2011: A Danish Cohort Study

Objective. By linkage of national registries, we investigated the risk of longterm sickness absence (LTSA) ≥ 3 weeks in a large cohort of Danish patients with rheumatoid arthritis (RA) and non-patients. The study aimed to (1) estimate the risk of LTSA for patients with RA compared with the general population, (2) examine whether the risk of LTSA has changed in recent years, and (3) evaluate the effect of other risk factors for LTSA (e.g., physical work demands, age, sex, education, and psychiatric and somatic comorbidities). Methods. A total of 6677 patients with RA aged 18–59 years in the years 1994–2011 were identified in registries and compared with 56,955 controls from the general population matched by age, sex, and city size. The risk of LTSA was analyzed using Cox proportional hazards models with late entry, controlling for other risk factors and assuming separate risks in the first year after diagnosis and the following years. Results. Compared with the general population, patients with RA had increased risk of LTSA in the first year after diagnosis (HR 5.4 during 1994–1999, 95% CI 4.2–6.8) and in following years (HR 2.4, 95% CI 2.1–2.8). For established RA (> 1 yr after diagnosis), the excess was 20% lower in 2006–2011 (HR 1.9, 95% CI 1.7–2.2) compared with 1994–1999 (p < 0.001). For patients with RA and controls, older age, shorter education, a physically demanding job, and somatic and/or psychiatric comorbidities increased the risk of LTSA. Conclusion. While improvements were observed from 1994–1999 to 2006–2011, patients with RA have significant increased risk of LTSA, in particular in the first year after diagnosis.

Effect of a Participatory Organizational-Level Occupational Health Intervention on Short-Term Sickness Absence: A Cluster Randomized Controlled Trial

OBJECTIVES The aim of this study was to examine whether employees in pre-schools that implemented a participatory organizational-level intervention focusing on the core task at work had a lower incidence of short-term sickness absence compared to employees in the control group. METHODS The cluster randomized controlled trial (RCT) comprised 78 pre-schools that were allocated to the intervention (44 pre-schools with 1760 employees) or control (34 pre-schools with 1279 employees) group. The intervention lasted 25 months and followed a stepwise and structured approach, consisting of seminars, workshops, and workplace-directed intervention activities focusing on the core task at work. Using Poisson regression, we tested differences in incidence rates in short-term sickness absence between the intervention and control groups during a 29-months follow-up. RESULTS Estimated short-term sickness absence days per person-year during follow-up were 8.68 and 9.17 in the intervention and control groups, respectively. The rate ratio (RR) for comparing incident sickness absence in the intervention to control groups during follow-up was 0.93 [95% confidence interval (95% CI) 0.86-1.00] in the crude analysis and 0.89 (95% CI 0.83-0.96) when adjusting for age, sex, job group, type and size of workplace, and workplace average level of previous short-term sickness absence. A supplementary analysis showed that the intervention also was associated with a reduced risk of long-term sickness absence with a crude RR of 0.83 (95% CI 0.69-0.99) and an adjusted RR of 0.84 (95% CI 0.69-1.01). CONCLUSIONS Pre-school employees participating in an organizational-level occupational health intervention focusing on the core task at work had a lower incidence of short-term sickness absence during a 29-month follow-up compared with control group employees.

Prediction of future labour market outcome in a cohort of long-term sick- listed Danes

BackgroundTargeted interventions for the long-term sick-listed may prevent permanent exclusion from the labour force. We aimed to develop a prediction method for identifying high risk groups for continued or recurrent long-term sickness absence, unemployment, or disability among persons on long-term sick leave.MethodsWe obtained individual characteristics and follow-up data from the Danish Register of Sickness Absence Compensation Benefits and Social Transfer Payments (RSS) during 2004 to 2010 for 189,279 Danes who experienced a period of long-term sickness absence (4+ weeks). In a learning data set, statistical prediction methods were built using logistic regression and a discrete event simulation approach for a one year prediction horizon. Personalized risk profiles were obtained for five outcomes: employment, unemployment, recurrent sickness absence, continuous long-term sickness absence, and early retirement from the labour market. Predictor variables included gender, age, socio-economic position, job type, chronic disease status, history of sickness absence, and prior history of unemployment. Separate models were built for times of economic growth (2005–2007) and times of recession (2008–2010). The accuracy of the prediction models was assessed with analyses of Receiver Operating Characteristic (ROC) curves and the Brier score in an independent validation data set.ResultsIn comparison with a null model which ignored the predictor variables, logistic regression achieved only moderate prediction accuracy for the five outcome states. Results obtained with discrete event simulation were comparable with logistic regression.ConclusionsOnly moderate prediction accuracy could be achieved using the selected information from the Danish register RSS. Other variables need to be included in order to establish a prediction method which provides more accurate risk profiles for long-term sick-listed persons.

Effect of a participatory organizational-level occupational health intervention on job satisfaction, exhaustion and sleep disturbances: results of a cluster randomized controlled trial

BackgroundWe examined whether the implementation of a participatory organizational-level intervention aiming to improve the working environment with a focus on the core task at work, increased job satisfaction and reduced exhaustion and sleep disturbances among pre-school employees.MethodsThe study sample consisted of 41 intervention group pre-schools with 423 employees and 30 control group pre-schools with 241 employees. The intervention lasted 25 months and consisted of seminars, workshops, and workplace specific intervention activities that were developed by focusing on the core task at work. We analyzed within-group changes in the three outcome variables from baseline to follow-up with t-tests for paired samples, separately for intervention and control group. Between-group differences in changes in the three outcome variables were analyzed using a mixed model with a repeated statement to account for the clustering effect of workplaces.ResultsWithin-group analyses showed that exhaustion decreased statistically significantly in both the intervention and the control group. There were no statistically significantly changes in job satisfaction and sleep disturbances. Between-group analyses showed that there was no statistically significant difference between the two groups for changes in any of the outcome variables, neither in the unadjusted or in the adjusted analyses.ConclusionsWe found no evidence that participating in an organizational-level occupational health intervention aiming to improve the working environment with a focus on the core task at work has an effect on pre-school employees’ job satisfaction, exhaustion and sleep disturbances.Trial registrationISRCTN16271504, November 15, 2016.

Visualizing Transitions between Multiple StatesâÂÂIllustrated by Analysis of Social Transfer Payments

Background: Multi-state analyses are used increasingly in areas such as economic, medical, and social research. They provide a powerful analysis for situations where the research subjects move between several distinct states, but results are often complex. The purpose of the current paper is to present a simple descriptive analysis to visualize patterns in the transitions: the Top10 chart. Data on social transfer payments are used to illustrate the approach. Methods: spent in each state, and is constructed from individual level data. Persons with the same pattern of transitions between states are grouped together and average durations are calculated. We analyzed data from 4950 Danish employees aged 18-59 years who, during two years of follow-up, could at any time be in one of seven mutually exclusive states: work, unemployment, sick-listing, studying, parent leave, disability pension, and an absorbing state consisting of those who died, retried, or emigrated. Results: The 10 most frequent transitional patterns described 84% of all women and 90% of all men in the sample. For women, the typical patterns involved working throughout the study (61.7%), patterns with sick-listing (12.0%), patterns with unemployment (5.3%), patterns with parent leave (3.6%), and studying (1.5%). For men, the typical patterns involved working throughout (68.8%), sick-listing (9.1%), unemployment (4.7%), parent leave (5.2%), and studying (0.9%). Conclusion: The Top10 chart provides a simple descriptive visualization of complex transitional patterns.

Work ability in rheumatoid arthritis patients: a register study on the prospective risk of exclusion and probability of returning to work

Objectives The aim was to study work ability in patients with RA compared with the general population by investigating the rates and risks of long-term sickness absence, unemployment and disability pension, and the chance of returning to work and the changes in these risks over time (1994-2011). Methods This was a cohort study with up to 17 years of follow-up (mean 6.95 years/person) including 6677 RA patients of working age (identified in the nationwide DANBIO registry) and 56 955 matched controls from the general population. A multi-state model was used to analyse all shifts between the work-related states (long-term sickness absence, unemployment and disability pension, as well as the chance of returning to work) and calculate hazard rates (HRs). Analyses were stratified by disease duration and controlled for socio-demographic factors, physical job exposure and somatic and psychiatric co-morbidities. Results RA patients had increased risk of long-term sickness absence (e.g. early RA: HR = 4.00, 95% CI: 3.64, 4.30) and disability pension (e.g. established RA: HR = 2.75, 95% CI: 2.54, 2.98) relative to controls. From 1994-99 to 2006-11, a decrease in the effect of established RA was observed [long-term sickness absence: from HR = 2.25 (95% CI: 1.99, 2.54) to 1.63 (95% CI: 1.51, 1.75); and disability pension: from HR = 3.49 (95% CI: 2.83, 4.32) to 2.40 (95% CI: 2.15, 2.69)]. RA patients had a lower chance of returning to work from long-term sickness absence or unemployment (HR = 0.60, HR=0.80), and this did not change over time. Conclusion RA patients remain at high risk for long-term sickness absence and disability pension, despite a positive development between 1996-99 and 2006-11. Returning to work after sick leave or unemployment remains a challenge for RA patients.