https://bmcpublichealth.biomedcentral.com/articles/10.1186/1471-2458-4-53
https://bmcpublichealth.biomedcentral.com/articles/10.1186/1471-2458-4-51
https://bmcpublichealth.biomedcentral.com/articles/10.1186/1471-2458-4-52
https://bmcpublichealth.biomedcentral.com/articles/10.1186/1471-2458-4-54
https://bmcpublichealth.biomedcentral.com/articles/10.1186/1471-2458-4-56
https://bmcpublichealth.biomedcentral.com/articles/10.1186/1471-2458-4-55
https://bmcpublichealth.biomedcentral.com/articles/10.1186/1471-2458-4-57
https://bmcpublichealth.biomedcentral.com/articles/10.1186/1471-2458-4-50