Epidemiological Studies Based on Small Sample Sizes – A Statistician's Point of View

<p/> <p>We consider 3 basic steps in a study, which have relevance for the statistical analysis. They are: study design, data quality, and statistical analysis. While statistical analysis is often considered an important issue in the literature and the choice of statistical method receives much attention, less emphasis seems to be put on study design and necessary sample sizes. Finally, a very important step, namely assessment and validation of the quality of the data collected seems to be completely overlooked.</p> <p>Examples from veterinary epidemiological research and recommendations for each step are given together with relevant references to the literature.</p

Joint mapping of cardiovascular diseases:comparing the geographic patterns in incident acute myocardial infarction, stroke and atrial fibrillation, a Danish register-based cohort study 2014–15

BACKGROUND: Disease mapping aims at identifying geographic patterns in disease. This may provide a better understanding of disease aetiology and risk factors as well as enable targeted prevention and allocation of resources. Joint mapping of multiple diseases may lead to improved insights since e.g. similarities and differences between geographic patterns may reflect shared and disease-specific determinants of disease. The objective of this study was to compare the geographic patterns in incident acute myocardial infarction (AMI), stroke and atrial fibrillation (AF) using the unique, population-based Danish register data. METHODS: Incident AMI, stroke and AF was modelled by a multivariate Poisson model including a disease-specific random effect of municipality modelled by a multivariate conditionally autoregressive (MCAR) structure. Analyses were adjusted for age, sex and income. RESULTS: The study included 3.5 million adults contributing 6.8 million person-years. In total, 18,349 incident cases of AMI, 28,006 incident cases of stroke, and 39,040 incident cases of AF occurred. Estimated municipality-specific standardized incidence rates ranged from 0.76 to 1.35 for AMI, from 0.79 to 1.38 for stroke, and from 0.85 to 1.24 for AF. In all diseases, geographic variation with clusters of high or low risk of disease after adjustment was seen. The geographic patterns displayed overall similarities between the diseases, with stroke and AF having the strongest resemblances. The most notable difference was observed in Copenhagen (high risk of stroke and AF, low risk of AMI). AF showed the least geographic variation. CONCLUSION: Using multiple-disease mapping, this study adds to the results of previous studies by enabling joint evaluation and comparison of the geographic patterns in AMI, stroke and AF. The simultaneous mapping of diseases displayed similarities and differences in occurrence that are non-assessable in traditional single-disease mapping studies. In addition to reflecting the fact that AF is a strong risk factor for stroke, the results suggested that AMI, stroke and AF share some, but not all environmental risk factors after accounting for age, sex and income (indicator of lifestyle and health behaviour). SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12942-021-00294-w

Long-Term Cardiovascular Health After Pregnancy in Danish Women With Congenital Heart Disease. A Register-Based Cohort Study Between 1993 and 2016

Background Little is known about the impact of pregnancy on long‐term cardiovascular health in individuals with congenital heart disease (CHD). We aimed to determine if giving birth in patients with CHD is associated with higher risk of long‐term cardiovascular morbidity. Methods and Results We studied a cohort of 1262 individuals with CHD giving birth (live or still) from 1993 to 2015 using Danish nationwide registers. We randomly sampled a comparison cohort matched on age of women with CHD who had not given birth at the time. We balanced the 2 cohorts on baseline demographic (eg, education) and clinical variables (eg, CHD severity) using inverse probability of treatment weighting. Individuals were followed for critical (eg, heart failure), other cardiovascular morbidity (eg, arrhythmia), and cardiac surgery/interventions after pregnancy. Individuals were followed for median 6.0 years (interquartile range 3.2–9.2). Among individuals giving birth the incidence rate per 1000 person‐years was 1.6, 10.0, and 6.0 for critical and other cardiovascular morbidity and cardiac surgery, respectively. There was no overall difference in risk of neither critical and other cardiovascular morbidity nor cardiac surgery among individuals who gave birth and individuals who did not; adjusted hazard ratios (aHR) were 0.74 (95% CI, 0.37–1.48), 0.88 (95% CI, 0.65–1.19), and 0.78 (95% C,I 0.54–1.12), respectively. However, individuals with obstetric complications had a higher long‐term risk of other cardiovascular morbidity (aHR, 1.85; 95% CI, 1.07–3.20). Conclusions Giving birth seemed not to be associated with a higher risk of long‐term cardiovascular morbidity among women with CHD. However, individuals having obstetric complications had a higher risk of other cardiovascular morbidity in the long term

Patterns of Perceived Indoor Environment in Danish Homes

The indoor environment is composed of several exposures existing simultaneously. Therefore, it might be useful to combine exposures into common combined measures when used to assess the association with health. The aim of our study was to identify patterns of the perceived indoor environment. Data from the Danish Health and Morbidity Survey in the year 2000 were used. The perceived indoor environment was assessed using a questionnaire (e.g., annoyances from noise, draught, and stuffy air; 13 items in total). Factor analysis was used to explore the structure of relationships between these 13 items. Furthermore, groups of individuals with similar perceived indoor environment were identified using latent class analysis. A total of 16,688 individuals &ge;16 years participated. Their median age was 46 years. Four factors were extracted from the factor analysis. The factors were characterized by: (1) a mixture of items, (2) temperature, (3) traffic, and (4) neighbor noise. Moreover, three groups of individuals sharing the same perception of their indoor environment were identified. They were characterized by: a low (n = 14,829), moderate (n = 980), and large number of annoyances (n = 879). Observational studies need to take this correlation and clustering of perceived annoyances into account when studying associations between the indoor environment and health