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Interrupted time series (ITS) analysis is being increasingly used in epidemiology. Despite its growing popularity, there is a scarcity of guidance on power and sample size considerations within the ITS framework. Our aim of this study was to assess the statistical power to detect an intervention effect under various real-life ITS scenarios. ITS datasets were created using Monte Carlo simulations to generate cumulative incidence (outcome) values over time. We generated 1,000 datasets per scenario, varying the number of time points, average sample size per time point, average relative reduction post intervention, location of intervention in the time series, and reduction mediated via a 1) slope change and 2) step change. Performance measures included power and percentage bias. We found that sample size per time point had a large impact on power. Even in scenarios with 12 pre-intervention and 12 post-intervention time points with moderate intervention effect sizes, most analyses were underpowered if the sample size per time point was low. We conclude that various factors need to be collectively considered to ensure adequate power for an ITS study. We demonstrate a means of providing insight into underlying sample size requirements in ordinary least squares (OLS) ITS analysis of cumulative incidence measures, based on prespecified parameters and have developed Stata code to estimate this.

Mathias Ried-Larsen,1–3 Reimar W Thomsen,2,4 Klara Berencsi,4 Cecilie F Brinkløv,1,5 Charlotte Brøns,1,5 Laura S Valentiner,1,6 Kristian Karstoft,1,3 Henning Langberg,1,6 Allan A Vaag,1,2,5 Bente K Pedersen,1,3 Jens S Nielsen7 1Department of Infectious Diseases, Centre for Physical Activity Research, Rigshospitalet, University of Copenhagen, Copenhagen, 2The Danish Diabetes Academy, Odense University Hospital, Odense, 3Department of Infectious Diseases, Centre of Inflammation and Metabolism, Rigshospitalet, University of Copenhagen, Copenhagen, 4Department of Clinical Epidemiology, Aarhus University Hospital, Aarhus Nord, 5Department of Endocrinology (Diabetes and Metabolism), Rigshospitalet, University of Copenhagen, 6CopenRehab, Department of Public Health, Section of Social Medicine, University of Copenhagen, Copenhagen, 7Department of Endocrinology, Odense University Hospital, Odense, Denmark Abstract: Promoting physical activity is a first-line choice of treatment for patients with type 2 diabetes (T2D). However, there is a need for more effective tools and technologies to facilitate structured lifestyle interventions and to ensure a better compliance, sustainability, and health benefits of exercise training in patients with T2D. The InterWalk initiative and its innovative application (app) for smartphones described in this study were developed by the Danish Centre for Strategic Research in T2D aiming at implementing, testing, and validating interval walking in patients with T2D in Denmark. The interval walking training approach consists of repetitive 3-minute cycles of slow and fast walking with simultaneous intensity guiding, based on the exercise capacity of the user. The individual intensity during slow and fast walking is determined by a short initial self-conducted and audio-guided fitness test, which combined with automated audio instructions strives to motivate the individual to adjust the intensity to the predetermined individualized walking intensities. The InterWalk app data are collected prospectively from all users and will be linked to the unique Danish nationwide databases and administrative registries, allowing extensive epidemiological studies of exercise in patients with T2D, such as the level of adherence to InterWalk training and long-term effectiveness surveys of important health outcomes, including cardiovascular morbidity and mortality. Currently, the InterWalk app has been downloaded by >30,000 persons, and the achieved epidemiological data quality is encouraging. Of the 9,466 persons providing personal information, 80% of the men and 62% women were overweight or obese (body mass index ≥25). The InterWalk project represents a contemporary technology-driven public health approach to monitor real-life exercise adherence and to propagate improved health through exercise intervention in T2D and in the general population. Keywords: exercise, telemedicine, cell phones

Anil Mor, Sinna P Ulrichsen, Elisabeth Svensson, Klara Berencsi, Reimar W Thomsen Department of Clinical Epidemiology, Institute of Clinical Medicine, Aarhus University Hospital, Aarhus, Denmark Background: To reduce the increasing burden of pneumonia hospitalizations, we need to understand their determinants. Being married may decrease the risk of severe infections, due to better social support and healthier lifestyle. Patients and methods: In this population-based case-control study, we identified all adult patients with a first-time pneumonia-related hospitalization between 1994 and 2008 in Northern Denmark. For each case, ten sex- and age-matched population controls were selected from Denmark's Civil Registration System. We performed conditional logistic regression analysis to estimate the odds ratios (ORs) for pneumonia hospitalization among persons who were divorced, widowed, or never married, as compared with married persons, adjusting for age, sex, 19 different comorbidities, alcoholism-related conditions, immunosuppressant use, urbanization, and living with small children. Results: The study included 67,162 patients with a pneumonia-related hospitalization and 671,620 matched population controls. Compared with controls, the pneumonia patients were more likely to be divorced (10% versus 7%) or never married (13% versus 11%). Divorced and never-married patients were much more likely to have previous diagnoses of alcoholism-related conditions (18% and 11%, respectively) compared with married (3%) and widowed (6%) patients. The adjusted OR for pneumonia-related hospitalization was increased, at 1.29 (95% confidence interval [CI]: 1.25-1.33) among divorced; 1.15 (95% CI: 1.12-1.17) among widowed; and 1.33 (95% CI: 1.29-1.37) among never-married individuals as compared with those who were married. Conclusion: Married individuals have a decreased risk of being hospitalized with pneumonia compared with never-married, divorced, and widowed patients. Keywords: marital status, risk, mortality, immune function