Stress and cancer: Nordic pieces to the complex puzzle

Excerpt

Using population and health registers to address critical research questions on determinants of health has become a unique contribution of the Nordic countries, largely thanks to the personal identification numbers (PINs) assigned to every inhabitant at birth or upon the time of immigration to the Nordic countries. Given the wide use by authorities, healthcare providers, and schools, the PINs enable unique record linkages between registers of the population and different health-related outcomes, resulting in a virtually complete and nationwide follow-up of all inhabitants in these countries. Since the registers are mainly set up for administrative or healthcare related purposes, the information collected is by definition prospective and independent of the later formulated research questions. Register-based studies therefore usually possess notably reduced risks for selection and information biases. Provided with nationwide study samples and often long periods of registration history, register-based studies further have the privilege of sufficient statistical power to address research questions engaging rare exposures and rare outcomes. The most important challenge of register-based studies is however the lack of detailed information on potential confounders—usually behavioral factors, sometimes leading to the inability to disentangle real associations from unmeasured confounders. However, the growing number of registers and amount of information collected in these registers, together with the recent methodological developments (e.g., quasi-experimental and within-subject designs) has rapidly reduced concerns of residual confounding. Moreover, the increasingly focused efforts in pooling identical registers across the Nordic countries have rendered a powerful resource for studies otherwise largely impossible in individual Nordic countries or settings outside Scandinavia. …