https://bmcmedresmethodol.biomedcentral.com/articles/10.1186/1471-2288-13-133 https://bmcmedresmethodol.biomedcentral.com/articles/10.1186/1471-2288-13-134 https://bmcmedresmethodol.biomedcentral.com/articles/10.1186/1471-2288-13-125 https://bmcmedresmethodol.biomedcentral.com/articles/10.1186/1471-2288-13-127 https://bmcmedresmethodol.biomedcentral.com/articles/10.1186/1471-2288-13-131 https://bmcmedresmethodol.biomedcentral.com/articles/10.1186/1471-2288-13-129 https://bmcmedresmethodol.biomedcentral.com/articles/10.1186/1471-2288-13-122 https://bmcmedresmethodol.biomedcentral.com/articles/10.1186/1471-2288-13-124 https://bmcmedresmethodol.biomedcentral.com/articles/10.1186/1471-2288-13-126 https://bmcmedresmethodol.biomedcentral.com/articles/10.1186/1471-2288-13-130 https://bmcmedresmethodol.biomedcentral.com/articles/10.1186/1471-2288-13-128 https://bmcmedresmethodol.biomedcentral.com/articles/10.1186/1471-2288-13-132 https://bmcmedresmethodol.biomedcentral.com/articles/10.1186/1471-2288-13-121 https://bmcmedresmethodol.biomedcentral.com/articles/10.1186/1471-2288-13-123