Farquhar Cynthia M, Showell Marian G, Showell Emily A E, Beetham Penny, Baak Nora, Mourad Selma, Jordan Vanessa M B
Department of Obstetrics and Gynaecology, Private Bag 92019, University of Auckland, Auckland 1142, New Zealand.
Department of Obstetrics and Gynaecology, Private Bag 92019, University of Auckland, Auckland 1142, New Zealand.
J Clin Epidemiol. 2017 Apr;84:47-53. doi: 10.1016/j.jclinepi.2016.11.011. Epub 2017 Jan 11.
To determine the prevalence of registered trials and to evaluate the risk of bias between registered and unregistered clinical trials.
The Cochrane Gynecology and Fertility Group's specialized register was searched on November 5, 2015, for randomized controlled trials published from 2010 to 2014. Studies were selected if they had randomized women or men for fertility treatments, were published in full text and written in English. Two reviewers then independently assessed trial registration status for each trial, by searching the publication, trial registries, and by contacting the original authors.
Of 693 eligible randomized controlled trials, only 44% were found to be registered. Unregistered clinical trials had smaller sample sizes than registered trials (P < 0.001). A random subsample of 125 registered and 125 unregistered trials was assessed for risk of bias using five of the Cochrane Risk of Bias "domains." Registered and unregistered trials differed in their risk of bias for random sequence generation (P = 0.001), allocation concealment (P = 0.003), and selective reporting (P < 0.001) but not blinding or incomplete outcome data (P > 0.05) domains. Only 54 (43.2%) of the 125 registered trials were registered prospectively. This study has the following limitations. Only English language trials were included in this review. We were unable to obtain protocols for the unregistered trials and therefore were unable to assess the risk of bias in the selective reporting domain.
All available trials should be included in systematic reviews and assessed for risk of bias as there are both registered trials with high risk of bias and unregistered trials with low risk of bias and by excluding unregistered trials more than half of the available evidence will be lost.
确定注册试验的患病率，并评估注册和未注册临床试验之间的偏倚风险。
2015年11月5日检索了Cochrane妇产科和生育组的专业注册库，以查找2010年至2014年发表的随机对照试验。入选的研究需为针对生育治疗对女性或男性进行随机分组、全文发表且为英文撰写。然后两名评审员通过检索出版物、试验注册库并联系原始作者，独立评估每个试验的注册状态。
在693项符合条件的随机对照试验中，仅44%被发现已注册。未注册的临床试验样本量比注册试验小（P<0.001）。使用Cochrane偏倚风险“领域”中的五个领域，对125项注册试验和125项未注册试验的随机子样本进行偏倚风险评估。注册和未注册试验在随机序列生成（P = 0.001）、分配隐藏（P = 0.003）和选择性报告（P<0.001）方面的偏倚风险不同，但在盲法或不完整结局数据（P>0.05）领域没有差异。125项注册试验中只有54项（43.2%）是前瞻性注册的。本研究有以下局限性。本综述仅纳入了英文试验。我们无法获取未注册试验的方案文本，因此无法评估选择性报告领域的偏倚风险。
所有可用试验均应纳入系统评价并评估偏倚风险，因为既有偏倚风险高的注册试验，也有偏倚风险低的未注册试验，且排除未注册试验将损失一半以上的可用证据。
