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Many would probably be content to use Bayesian methodology for hypothesis testing, if it was easy, objective and with trustworthy assumptions. The Bayesian information criterion and some simple bounds on Bayes factor are closest to fit this bill, but with clear limitations. Here we develop an approximation of the so-called Bayes factor applicable in any bio-statistical settings where we have a d-dimensional parameter estimate of interest and the d x d dimensional (co-)variance of it. By design the approximation is monotone in the p value. It it thus a tool to transform p values into evidence (probabilities of the null and the alternative hypothesis, respectively). It is an improvement on the aforementioned techniques by being more flexible, intuitive and versatile but just as easy to calculate, requiring only statistics that will typically be available: e.g. a p value or test statistic and the dimension of the alternative hypothesis.

Using provisional or opportunistic data, three nationwide studies (The Netherlands, the USA and Denmark) have identified a reduction in preterm or extremely preterm births during periods of COVID-19 restrictions. However, none of the studies accounted for perinatal deaths. To determine whether the reduction in extremely preterm births, observed in Denmark during the COVID-19 lockdown, could be the result of an increase in perinatal deaths and to assess the impact of extended COVID-19 restrictions, we performed a nationwide Danish register-based prevalence proportion study. We examined all singleton pregnancies delivered in Denmark during the COVID-19 strict lockdown calendar periods (March 12–April 14, 2015-2020, N = 31,164 births) and the extended calendar periods of COVID-19 restrictions (February 27–September 30, 2015-2020, N = 214,862 births). The extremely preterm birth rate was reduced (OR 0.27, 95% CI 0.07 to 0.86) during the strict lockdown period in 2020, while perinatal mortality was not significantly different. During the extended period of restrictions in 2020, the extremely preterm birth rate was marginally reduced, and a significant reduction in the stillbirth rate (OR 0.69, 0.50 to 0.95) was observed. No changes in early neonatal mortality rates were found.Conclusion: Stillbirth and extremely preterm birth rates were reduced in Denmark during the period of COVID-19 restrictions and lockdown, respectively, suggesting that aspects of these containment and control measures confer an element of protection. The present observational study does not allow for causal inference; however, the results support the design of studies to ascertain whether behavioural or social changes for pregnant women may improve pregnancy outcomes. What is Known:• The aetiologies of preterm birth and stillbirth are multifaceted and linked to a wide range of socio-demographic, medical, obstetric, foetal, psychosocial and environmental factors.• The COVID-19 lockdown saw a reduction in extremely preterm births in Denmark and other high-income countries. An urgent question is whether this reduction can be explained by increased perinatal mortality. What is New:• The reduction in extremely preterm births during the Danish COVID-19 lockdown was not a consequence of increased perinatal mortality, which remained unchanged during this period.• The stillbirth rate was reduced throughout the extended period of COVID-19 restrictions.

PURPOSE: In pharmacoepidemiology, correctly defining the exposure period of pharmacological treatment is a challenging step when information on the time in treatment is missing or incomplete.METHODS: In this review, we describe several methods for defining exposure to pharmacological treatments using secondary data sources that lack such information.RESULTS AND CONCLUSION: Several methods for assessing the duration of redeemed prescriptions and combining them into temporal sequences are available. We present a set of considerations to make researchers aware of the potentials and pitfalls of these methods that may aid in minimizing biases in research using these methods. Additionally, we highlight that, to date, there is no one-size-fits-all solution. Thus, the choice of method should be based on their area of applicability combined with a careful mapping to the research scenario under investigation.

Chronic lymphocytic leukemia (CLL) is accompanied by increased risk of potentially fatal infections. While this can mostly be attributed to disease-related immune dysfunction, it is not known if CLL patients are also constitutionally susceptible to infections. We linked nation-wide Danish registers to explore this possibility, approximating infection susceptibility by use of antimicrobials. We assessed the incidence of antimicrobials among CLL patients and matched controls from the general population for up to 22 years before index diagnosis, and among children and grandchildren of CLL patients and their matched controls. Our analyses showed that for CLL patients overall antimicrobial use began to increase gradually six years before leukemia diagnosis. Before this time point, CLL patients had used significantly more macrolides (relative risk = 1.15; 95% confidence interval 1.10-1.20), antimycotics (1.18; 1.08-1.30), and antivirals (1.62; 1.45-1.81) than controls for up to 22 years before diagnosis. The same pattern of increased use was found among CLL patients' children and grandchildren. Our study suggests that CLL diagnosis is preceded by decades of increased susceptibility to infections. The duration of this time window is compatible with causal roles of immune dysfunction and/or certain infections in CLL pathogenesis, possibly mediating the association between constitutional infection susceptibility and CLL risk.

Background The present study aimed to assess whether the widespread concern of inferior cancer survival in adolescents and young adults (AYAs) compared with children and adults holds true in a Nordic setting with important differences in healthcare organisation compared with the United States (e.g. free access to healthcare) and the United Kingdom (e.g. young teenagers are treated in paediatric departments). Methods Five-year relative survival was calculated for 17 diagnostic groups in patients diagnosed in 2000–2013 in three diagnostic age categories: children (0–14 years), AYAs (15–24 years) and adults (25–34 years). Results For 13 out of 17 diagnostic groups examined, there was no difference in survival between AYAs and neighbouring age categories. For acute lymphoblastic leukaemias, astrocytomas, rhabdomyosarcomas and non-rhabdomyosarcoma soft tissue sarcomas we found survival in children to be superior to that in AYAs. For these four diagnostic groups, the rate of survival improvement over three calendar periods (1980–1989, 1990–1999 and 2000–2013) was not particularly low in AYAs compared with neighbouring age categories. Conclusions The present study suggests that in an affluent setting with free access to healthcare, meaningful differences in survival between AYA patients and either childhood or adult patients are a phenomenon of the past for most AYA cancer diagnostic groups.

Objective: Clinical databases have been invented to monitor treatment outcomes, therapies or diseases, often in great detail. The traditional population-based cancer registry has been invented to collect a minimum of information about all incident cancers. Do clinical databases render population-based cancer registers obsolete as sources of cancer cases for epidemiological study? Methods: We compared the study base of first incident breast cancer cases in Denmark in 1978–1994 known from the national cancer register and from the national clinical database on breast cancer patients. The clinical database is used for monitoring protocoled treatment. Results: Combining the two data sources we found 48,522 first primary breast cancers in Denmark 1978–1994. Of these, 37,640 were included in both data sources, 2151 were included only in the clinical database, and 8731 were included only in the cancer register. A major part of the difference between the two data sources was due to treatment-focused data collection in the clinical database, and a minor part due to differences in the registration of second primaries, date of diagnosis and invasiveness. Conclusions: Cancer incidence data are sensitive to registration procedures and definitions. Clinical cancer databases cannot generally replace the traditional cancer register as a reliable data source for incident cancer cases in a national population.