Never plan a population based cohort study on a rainy Friday after a sunny Thursday

Many cohort studies have identified factors leading to higher attrition or drop-out rates of study subjects. Low educational level, low household income or participant’s gender are such known factors [1, 2]. But no study to our knowledge has addressed the influence of weather conditions or general cultural factors on the rate of missed or canceled study appointments. After 1 year of experience with the LIFE (Leipzig Research Centre for Civilization Diseases) Child study cohort and about 1,000 study appointments we analyzed our data and identified such general factors. The LIFE Child study is a large prospective population based cohort study of children and adolescents in Leipzig (Germany). We plan to recruit 10,000 children from fetal life to age 18 years with annual followup examinations over 10 years. Our aim is to understand what mechanisms and mediators be it (epi)genetic, metabolic or environmental influence health and development of children and adolescents in modern societies. Details of the study protocol have been published elsewhere [8]. A typical day in the study center comprises of a general pediatric and dental examination, anthropometric measurements, a collection of blood, hair and urine samples and various tests e.g. motoric skills tests, voice examination, ECG or ultrasonography. After pilot and validation studies the main program has started in July 2011. Children of the city of Leipzig were recruited using different strategies such as announcements in local kindergartens, schools, newspapers, websites and by the support of local health authorities. Families being interested in the study program fill out a contact form. Then the study office team schedules an appointment via phone. Nine hundred twentyone first-contact appointments were made between 08/01/ 2011 and 07/31/2012. Within this time period 30 appointments were missed (3.26 %) and 134 were canceled (14.55 %). Accordingly, the overall first-contact drop-out rate was 17.81 %. A higher risk of first-contact drop-out was found on Fridays compared to Mondays (OR = 1.79, p = 0.045). We also found an influence of specific weather conditions: Drop-outs increased with higher sunshine duration at the day before the appointment (OR per hour sunshine = 1.04, p = 0.027), when the day of appointment was rainy (precipitation [0 mm, OR = 1.39, p = 0.056) or when the outside temperature at the day of the appointment was higher than the 10-year mean (OR per degree 1.06, p = 0.037) [weather data were received from Deutscher Wetterdienst (www.dwd.de)]. We found no influence on missed or canceled first-contact appointments in relation to other weekdays, sunshine duration at the day of the appointment, precipitation at the day before the appointment, the age of the children or schooldays versus holidays. Because only first-contact appointments were analyzed data about the subjects like social status are not available at this point. In autumn 2013 we will focus on missed follow-up appointments and will be able to report This study was conducted for the LIFE Child Study Investigators.