BACKGROUND Extensive recruitment effort at baseline increases representativeness of study populations by decreasing non-response and associated bias. First, it is not known to what extent increased attrition occurs during subsequent measurement waves among subjects who were hard-to-recruit at baseline and what characteristics the hard-to-recruit dropouts have compared to the hard-to-recruit ret...

Humans collaborate with non-kin in special ways, but the evolutionary foundations of these collaborative skills remain unclear. We presented chimpanzees with collaboration problems in which they had to decide when to recruit a partner and which potential partner to recruit. In an initial study, individuals recruited a collaborator only when solving the problem required collaboration. In a secon...

Method Patients with nasal polyps were recruited from the clinic, adult first-degree relatives of the patients were asked to participate. Our intention was to recruit one relative of each gender per patient. All participants were examined with nasal endoscopy and underwent a structured interview regarding upper airway symptoms and risk factors. The results were compared with a general populatio...