Using multiple sources to improve and measure case ascertainment in surveillance studies: 20 years of the British Paediatric Surveillance Unit

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Abstract
Background The British Paediatric Surveillance Unit (BPSU) was established in 1986 to facilitate national surveillance of uncommon paediatric disorders. This study investigated the effectiveness of using multiple source reporting and capture–recapture analysis to maximize case ascertainment in studies undertaken through the BPSU. Methods Structured review of all surveillance studies completed through the BPSU. Quantitative and qualitative analysis of the effectiveness of multiple reporting sources and capture–recapture methods was made. Results Of 71 studies undertaken through the BPSU, 59 were included in this review and 38 used additional data sources. Established national sources were most readily adapted for use as secondary data sources, including routine health data, communicable disease and specialty-specific surveillance units, whilst the involvement of parent groups and the media was less successful. Six studies employed capture–recapture techniques to estimate the completeness of case ascertainment. Conclusions Active surveillance through the BPSU remains a timely and reliable primary source of cases, but employing additional reporting sources is effective in enhancing case ascertainment. When the assumptions for its valid use are met, capture–recapture analysis allows the estimation of completeness of ascertainment. It is essential to define the purpose of an additional source at the outset of a study and to ensure that subsequent analysis is appropriate.