Figure 1.

The overall LongGerd study project flowchart showing the steps with the postal Abdominal Symptom Questionnaire (ASQ) surveys targeting equally sampled samples of the adults in the Östhammar community, Sweden, on four occasions, and the subsample studies on two occasions analysed in this study: the first on Helicobacter pylori (H. pylori) serology in 1989 (n = 145) and the second on H. pylori detected by both serology and histology in 2012 (n = 388). The sample approached by mail in 1989 originates from the 1988 mail study. The 1995 mail study is included to visualise the complete sampling procedure, as individuals for the 2011 study (n = 305 as shown in Figure 2) were recruited here. The two parts of the project used in this study are highlighted in dark blue. Target population size, response rate and age range and gender distribution in responders are also shown. OEGD = oesphagogastroduodenoscopy.