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Arbets- och Miljömedicin

Medicinska fakulteten | Lunds universitet

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Jonas Björk

Professor in Epidemiology

 

Jonas Björk

 

 

 Department
 Phone
 E-mail

 Division of occupational and environmental medicine
 +46 - 46 - 222 69 16 
 jonas.bjork@med.lu.se 

Publication list

A complete publication list can be found here.

Current methodological projects

Longitudinal data analysis

Results of observational studies are often used as a basis for public health interventions, e.g. investments in neighborhood facilities aiming at reducing social inequalities in well-being and health. It is essential that the scientific basis for such decisions is sound. In this project we will explore methodological issues in design and analysis of longitudinal studies with a series of simultaneous assessments of both exposure and outcome. Such designs are often survey-based and are increasingly used in order to overcome the well-known limitations of cross-sectional studies, but remaining validity issues related to self-selection, reversed causality and time-varying confounding deserve careful attention. Moreover, representation and analysis of longitudinal data differ noticeably across studies, often with unknown consequences for the validity of the results.

Propensity stratification

It is often of special interest to identify subgroups, defined by e.g. genetic, environmental and/or social factors, where the exposure under investigations is particularly predictive of health and well-being. Analyzing such heterogeneity in registry-based studies is challenging, since the number of individual trajectories that could potentially modify the effect is likely to be numerous. Propensity scores techniques have since their introduction evolved into a formal step-by-step procedure for confounding control, through stratification (or similar types of adjustments) based on the exposure propensity. In on-going work we study stratification for outcome propensity (also known as a prognostic score or as risk stratification) as a means of investigating heterogeneity of exposure effects while keeping the number of subgroups limited. This approach is potentially useful for assessing individual susceptibility to environmental exposures, but practical concerns with outcome propensity modeling as well as the theoretical properties of such modeling warrant further investigation.

Spatial reliability analysis

Comparisons of perceived and objectively measured neighborhood attributes or exposures show associations (correlations) but generally low agreement. The low agreement has been explained as a mismatch between perceptions and objective facts, but may also suggest that perceived and objective measures are capturing different aspects of the local environment. Additionally, the instruments used to capture perception may lack inter- or intra-reliability, and thereby contributing to the low agreement with objectively measured attributes. In this project, we develop the use of kappa and colocation coefficients as tools to investigate the reliability of environmental ratings among nearest neighbors in a spatial context.

Books

Björk J. Praktisk statistik för medicin och hälsa. Liber 2011. (Practical statistics for medicine and health)

Link to book web page.

Scientific commissions

  • Assistant coordinator for SIMSAM Lund with grants from the Swedish Research Council (VR).
  • Member of the SBU-expert panel "Metoder för att skatta njurfunktionen" (Endogenous markers for estimation of kidney function), 2009 - 2011
    The report is available here. 

Useful links

Registry-based research in Sweden
http://registerforskning.se/

Seminars about methodological issues in registry-based research
 http://www.med.lu.se/simsam_lund/seminars

Equator Network - guidelines for transparent reporting of health research
http://www.equator-network.org/

Points of significance in Nature
http://go.nature.com/xlj9lr

Statistics notes in BMJ
http://www.medcalc.org/literature_notes.php

Free software for sample size calculations
http://biostat.mc.vanderbilt.edu/twiki/bin/view/Main/PowerSampleSize

Verktyg för klinisk forskning i Läkartidningen (Swedish)
 http://www.lakartidningen.se/Samlingssidor/Serie-Verktyg-for-klinisk-forskning/