Research in rural regions for rural regions: Temporary study centers as a method to increase response in population-based studies. Results of the German national cohort in Mecklenburg-Western Pomerania

Abstract

Background Scientific impact of populations-based cohort studies crucially depends on adequate response. Response varies widely and is affected by various factors e.g. time and costs involved for study participation. Both of them will usually increase with an increasing distance between study center and place of residence. The study region Mecklenburg-Western Pomerania is the least densely populated region abundant with water and one of the economically weakest states in Germany (area: approximately 23,000 km2, population: approximately 1.7 million). Therefore, the present study examines the effect of successive implementation of temporary study centers on response embedded in a rural and sparsely populated region within the setting of the German National Cohort. Methods The German National Cohort is a population-based, epidemiologic study comprising 200,000 randomly assigned women and men (age range: 20–69 years, baseline: 2014–2019) examined in 18 study centers in Germany. Within the study region Mecklenburg-Western Pomerania, 20,000 participants will be recruited. To address the frictional effect of distance on response, we used geographical data (postal code, district code, city name, and population densities) to determine locations for study centers with an optimal distance and a maximum number of potentially reachable participants. On that basis, we established beside a permanent study center [with whole-body magnetic resonance imaging (MRI)] temporary study centers one by one with equivalent facilities for a standardized data collection, uniquely in the German National Cohort. Study invitations are issued for the nearest-by study center in accordance to place of residence of the potential participants. Distances, response, and sample fractions within the study population were analyzed. Results A total of n = 17,746/20,000 participants were examined so far (nationwide: n = 140,578/200,000). Thereof, n = 8,140/10,000 participants within the permanent study center embedded in the middle of the recruitment region in the city of Neubrandenburg (year 2015–present). n = 9606/10,000 participants were examined in one of the three temporary centers successively established in the city of Neustrelitz (n = 3215, year 2014–2016), city of Waren/Mueritz (n = 4885, year 2016–2017) and city of Demmin (n = 1506, year 2017–present). Mean distances to the nearest-by study center vary between 23.2 km (permanent center) and 21.3 km (temporary centers). Obtained response varies between 20.7% (permanent study center) and 18.8% (temporary centers). Sampling fractions are high, in several age strata up to 80.0%. Conclusion In rural, sparsely populated regions of population-based studies, temporary study centers can minimize the response reducing effect of fraction of distance. Therefore, research in rural regions for rural regions will be feasible, despite the particular efforts (personal and financial resources) required for the implementation of such centers. MRI offered in the permanent center, may explain the slightly higher response there than for the temporary centers. As many characteristics of the study region Mecklenburg-Western Pomerania (e.g. less industrialization/economic changes due to a decline in birth rates and the migration of young and well educated people to metropolitan areas) are not limited to this region, effects observed in the present study may be predictive for many other European regions.