title: Representativeness of child controls recruited by random digit dialling.
abstract: Recruiting control subjects who are representative of the population from which the cases are drawn is a challenge in case-control studies. This paper examines the performance of random digit dialling (RDD) in obtaining a control sample, and the sample's representativeness of the population with respect to socio-economic status. The study subjects were recruited from 2003 to 2006 for a national, population-based case-control study investigating causes of acute lymphoblastic leukaemia (ALL) in children <15 years of age in Australia. Control families' addresses were linked to Australian Bureau of Statistics Census 2006 Collection Districts and thus to Socio-Economic Indexes for Area scores, which are area-based measures of socio-economic status. These scores were compared with those of all collection districts where families lived. We estimate that 55% of eligible families in the RDD sample agreed to participate in the study. Participation was directly related to socio-economic status with those of highest economic status most likely to participate. Completeness of participation in the components of data collection was similarly related to socio-economic status. This evidence of selection according to socio-economic status indicates that there may also be selection with respect to other factors potentially important in the aetiology of ALL.
authors.affiliation: Telethon Institute for Child Health Research, Centre for Child Health Research, University of Western Australia, Perth, WA, USA. helenb@ichr.uwa.edu.au
authors.forename: Helen D
authors.initials: HD
authors.lastname: Bailey
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Milne
authors.forename: Nicholas
authors.initials: N
authors.lastname: de Klerk
authors.forename: Lin
authors.initials: L
authors.lastname: Fritschi
authors.forename: Carol
authors.initials: C
authors.lastname: Bower
authors.forename: John
authors.initials: J
authors.lastname: Attia
authors.forename: Bruce K
authors.initials: BK
authors.lastname: Armstrong
mesh_terms: D016022:Case-Control Studies; D002648:Child; D002675:Child, Preschool; D003625:Data Collection; D005260:Female; D006801:Humans; D008297:Male; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000453:epidemiology*; D015983:Selection Bias; D012959:Socioeconomic Factors; D013689:Telephone