Threats to reliability risk erroneous conclusions: a survey of prospective registration and sample sizes of randomised trials in women's health.
OBJECTIVE
Prospective registration of clinical trials has been required since 2005. We aimed to assess concordance between registered and reported sample sizes among prospectively registered randomised controlled trials (RCTs) in obstetrics and gynaecology.


METHODS
Analysis of prospectively registered and published data.


METHODS
Women's health.


METHODS
Obstetrics and gynaecology RCTs published in eight journals in 2015.


METHODS
Specialist (Acta Obstet Gynecol Scand, BJOG, Obstet Gynecol and Am J Obstet Gynecol) and general (BMJ, N Engl J Med, JAMA and Lancet) journals were searched from 1 January to 31 December 2015 for main reports of obstetrics and gynaecology RCTs. Their corresponding registries and protocols were sought and data were extracted. Proportions and 95% CI were calculated using exact methods.


METHODS
Prospective registration of RCT and sample size concordance between RCTs and their registries within those where registration took place before patients were recruited.


RESULTS
Of the 75 relevant RCTs, 51 (68%, 95% CI 56-78%, P < 0.001 using a null hypothesis requiring 100% compliance) were prospectively registered, a feature found to be more common in general journals versus specialist journals (21/22 versus 30/53, 95% versus 57%, P = 0.001). Of the 51 prospectively registered RCTs, 31 (61%, 95% CI 46-74%, P = 0.003 using a null hypothesis requiring 40% of studies to achieve their stated sample size) did not reach the target sample size.


CONCLUSIONS
There are gaps in universal adoption of the prospective trial registration rule. Inability to meet target sample size risks deficiencies in statistical power with unreliability in results.


CONCLUSIONS
Only two-thirds of RCTs in women's health are prospectively registered, and over half fail to achieve target sample sizes.
Women's Health Research Unit, Centre for Primary Care and Public Health, Blizard Institute, Barts and The London School of Medicine and Dentistry, London, UK.
S K
SK
Nijjar
Women's Health Research Unit, Centre for Primary Care and Public Health, Blizard Institute, Barts and The London School of Medicine and Dentistry, London, UK.
K S
KS
Khan
D006176:Gynecology / Q000706:statistics & numerical data; D006801:Humans; D009774:Obstetrics / Q000706:statistics & numerical data; D011446:Prospective Studies; D016032:Randomized Controlled Trials as Topic / Q000706:statistics & numerical data*; D012042:Registries / Q000706:statistics & numerical data; D015203:Reproducibility of Results; D012306:Risk; D018401:Sample Size; D011795:Surveys and Questionnaires; D016387:Women's Health / Q000706:statistics & numerical data*
Protocols; randomised controlled trial; registries; sample size