A Note on Random Intensities and Conditional Survival Functions

One of the interesting directions of research in IIASA's Population Program deals with the methodological aspects of population heterogeneity dynamics. The crucial notion in this analysis is the stochastic intensity which is widely used in the stochastic processes models of human morbidity and mortality or technical failure. This paper provides the probabilistic specification of this notion which gives an opportunity to use the results of modern general theory of processes in analyzing factors that influence demographic characteristics

Reversing conditional orderings

We analyze some specific aspects concerning conditional orderings and relations among them. To this purpose we define a suitable concept of reversed conditional ordering and prove some related results. In particular we aim to compare the univariate stochastic orderings ≤ st, ≤ hr, and ≤ lr in terms of differences among different notions of conditional orderings. Some applications of our result to the analysis of positive dependence will be detailed. We concentrate attention to the case of a pair of scalar random variables X, Y ​. Suitable extensions to multivariate cases are possible

Leisure time physical activity in a 22-year follow-up among Finnish adults

BACKGROUND: The aim of this study was to explore long-term predictors of leisure time physical activity in the general population. METHODS: This study comprised 718 men and women who participated in the national Mini-Finland Health Survey from 1978–1980 and were re-examined in 2001. Participants were aged 30–80 at baseline. Measurements included interviews, health examinations, and self-administered questionnaires, with information on socioeconomic position, occupational and leisure time physical activity, physical fitness, body mass index, smoking, alcohol consumption, and physical functional capacity. Analyses included persons who were working and had no limitations in functional capacity at baseline. RESULTS: The strongest predictor of being physically active at the follow-up was participation in physical activity at baseline, with an OR 13.82 (95%CI 5.50-34.70) for 3 or more types of regular activity, OR 2.33 (95%CI 1.22-4.47) for 1–2 types of regular activity, and OR 3.26 (95%CI 2.07-5.15) for irregular activity, as compared to no activity. Other determinants for being physically active were moving upwards in occupational status, a high level of baseline occupational physical activity and remaining healthy weight during the follow-up. CONCLUSIONS: To prevent physical inactivity among older adults, it is important to promote physical activity already in young adulthood and in middle age and to emphasize the importance of participating in many types of physical activity

Comment on 'Using multiple observationally-based constraints to estimate climate sensitivity' by J. D. Annan and J. C. Hargreaves, Geophys. Res. Lett., 2006

Peer reviewe

Multisite musculoskeletal pain predicts medically certified disability retirement among Finns

BackgroundMusculoskeletal pain at several sites (multisite pain) is more common than single-site pain. Little is known on its effects on disability pension (DP) retirement. MethodsA nationally representative sample comprised 4071 Finns in the workforce aged 30 to 63. Data (questionnaire, interview, clinical examination) were gathered in 2000-2001 and linked with national DP registers for 2000-2011. Pain during the preceding month in 18 locations was combined into four sites (neck, upper limbs, low back, lower limbs). Hazard ratios (HR) of DP were estimated by Cox regression. ResultsThe HR of any DP (n=477) was 1.6 (95% confidence interval 1.2-2.1) for one, 2.5 (1.9-3.3) for two, 3.1 (2.3-4.3) for three and 5.6 (4.0-7.8) for four pain sites, when adjusted for age and gender. When additionally adjusted for clinically assessed chronic diseases, the HRs varied from 1.4 (1.0-1.8) to 3.5 (2.5-4.9), respectively. When further adjusted for physical and psychosocial workload, education, body mass index, smoking, exercise and sleep disorders, the HRs were 1.3 (0.9-1.7), 1.6 (1.2-2.2), 1.8 (1.3-2.5) and 2.5 (1.8-3.6). The number of pain sites was especially strong in predicting DPs due to musculoskeletal diseases (HRs in the full model; 3.1 to 4.3), but it also predicted DPs due to other somatic diseases (respective HRs 1.3 to 2.3); pain in all four sites was also predictive of DPs due to mental disorders (full model HR 2.2). ConclusionsThe number of pain sites independently predicted DP retirement. Employees with multisite pain may need specific support to maintain their work ability.Peer reviewe

Multisite musculoskeletal pain trajectories from midlife to old age : a 28-year follow-up of municipal employees

Objectives We studied the developmental trajectories of multisite musculoskeletal pain (MSP) to learn whether pain in midlife persists to old age, and whether pain trajectories associate with midlife work or lifestyle exposures or retirement from work. Methods Municipal employees aged 44–58 years were studied in 1981 (n=6257) with follow-ups in 1985, 1992, 1997 and 2009. Pain in the neck, low back, and upper and lower limbs was assessed in each survey. Trajectories of the number (0–4) of pain sites were defined using growth mixture modelling (n=3093). Workload, lifestyle and morbidity were elicited by questionnaire and retirement from registries. Associations of baseline factors with pain trajectories were assessed by multinomial logistic regression. Cumulative hazard curves for retirement by trajectory group were calculated. Results Three trajectories of pain over 28 years emerged: low (25%), moderate (52%) and high-decreasing (23%). In the latter, the number of pain sites first decreased sharply, stabilising to a moderate level after most subjects had retired. The disability pension rate was highest in this trajectory, which associated with high baseline morbidity, particularly musculoskeletal disorder (OR 8.06; 95% CI 5.97 to 10.87). Also high biomechanical exposure (2.86;95% CI 2.16 to 3.78), high job demands (1.79; 95% CI 1.39 to 2.30), high job control (OR 0.70; 95% CI 0.54 to 0.90), body mass index (BMI) ≥25.0 kg/m2 (1.40; 95% CI 1.09 to 1.80) and low leisure-time physical activity (LTPA) (1.39; 95% CI 1.09 to 1.78) at baseline were associated with this trajectory. However, high LTPA and BMI in repeated surveys also associated with the high-decreasing trajectory. Conclusion MSP in midlife often persists to old age. However, high widespreadness of pain may decrease with retirement from work.peerReviewe

Nonparametric estimation of conditional transition probabilities in a non-Markov illness-death model

One important goal in multi-state modeling is the estimation of transition probabilities. In longitudinal medical studies these quantities are particularly of interest since they allow for long-term predictions of the process. In recent years signi ficant contributions have been made regarding this topic. However, most of the approaches assume independent censoring and do not account for the influence of covariates. The goal of the paper is to introduce feasible estimation methods for the transition probabilities in an illness-death model conditionally on current or past covariate measures. All approaches are evaluated through a simulation study, leading to a comparison of two di erent estimators. The proposed methods are illustrated using real a colon cancer data set.This research was nanced by FEDER Funds through Programa Operacional Factores de Competitividade COMPETE and by Portuguese Funds through FCT - Funda ção para a Cência e a Tecnologia, within Projects Est-C/MAT/UI0013/2011 and PTDC/MAT/104879/2008. We also acknowledge nancial support from the project Grants MTM2008-03129 and MTM2011-23204 (FEDER support included) of the Spanish Ministerio de Ciencia e Innovaci on and 10PXIB300068PR of the Xunta de Galicia. Partial support from a grant from the US National Security Agency (H98230-11-1-0168) is greatly appreciated

Reconstructing promoter activity from Lux bioluminescent reporters

The bacterial Lux system is used as a gene expression reporter. It is fast, sensitive and non-destructive, enabling high frequency measurements. Originally developed for bacterial cells, it has also been adapted for eukaryotic cells, and can be used for whole cell biosensors, or in real time with live animals without the need for euthanasia. However, correct interpretation of bioluminescent data is limited: the bioluminescence is different from gene expression because of nonlinear molecular and enzyme dynamics of the Lux system. We have developed a computational approach that, for the first time, allows users of Lux assays to infer gene transcription levels from the light output. This approach is based upon a new mathematical model for Lux activity, that includes the actions of LuxAB, LuxEC and Fre, with improved mechanisms for all reactions, as well as synthesis and turn-over of Lux proteins. The model is calibrated with new experimental data for the LuxAB and Fre reactions from Photorhabdus luminescens --- the source of modern Lux reporters --- while literature data has been used for LuxEC. Importantly, the data show clear evidence for previously unreported product inhibition for the LuxAB reaction. Model simulations show that predicted bioluminescent profiles can be very different from changes in gene expression, with transient peaks of light output, very similar to light output seen in some experimental data sets. By incorporating the calibrated model into a Bayesian inference scheme, we can reverse engineer promoter activity from the bioluminescence. We show examples where a decrease in bioluminescence would be better interpreted as a switching off of the promoter, or where an increase in bioluminescence would be better interpreted as a longer period of gene expression. This approach could benefit all users of Lux technology