Blinding and exclusions after allocation in randomised controlled trials: survey of published parallel group trials in obstetrics and gynaecology

Schulz, Kenneth F.; Grimes, David A.; Altman, Douglas G.; Hayes, Richard

doi:10.1136/bmj.312.7033.742

Cited by 146 publications

(76 citation statements)

References 19 publications

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“…Studies similar to ours have been conducted in other specialties (3,(21)(22)(23)(24). These also show problems in the conduct and design of trials in other specialties.…”

Section: Discussionmentioning

confidence: 83%

The Number, Quality, and Coverage of Randomized Controlled Trials in Nephrology

Strippoli

Craig²,

Schena³

2004

Journal of the American Society of Nephrology

294

200

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Abstract. Randomized controlled trials (RCT) are the optimal study design to answer intervention questions. The authors evaluated the number, quality, and coverage of RCT in nephrology. MEDLINE was searched using the relevant medical subject headings for nephrology and 12 major specialties in internal medicine, limited by "randomized controlled trial" as a publication type. A random selection of 160 RCT in nephrology (40 for each decade) published since 1966 and an additional 270 RCT from ongoing or published Cochrane systematic reviews in various areas of nephrology, dialysis, and transplantation were evaluated for quality of reporting using standard criteria. The number of RCT published in nephrology from 1966 to 2002 (2779) is fewer than all other specialties of internal medicine (range: 5335 in hematology to 27109 in cardiology) with the proportion of all citations which are RCT being the third lowest (1.15%). There has been an increase in both indices from 1966 to 1996, but not at a greater rate than other specialties, and there has been no increase over the past 5 yr. Some areas of nephrology, in particular glomerulonephritis, are clear outliers with very low numbers of RCT to guide clinical decision-making. Overall the quality of RCT reporting in nephrology is low and has not improved over the past 30 yr with unclear allocation concealment (89%), lack of reported blinding of outcome assessors (92%), and failure to perform "intention-to-treat analysis" (50%) particularly frequent. The challenges of improving the quality and quantity of trials in nephrology are substantial, but they can be overcome by using standard guidelines and checklists for trial reporting, greater attention to the trial methods and not just the results, involving experts in trial design and reporting, multicenter collaboration, and larger and simpler trials.Because randomized controlled trials (RCT) are designed to provide unconfounded estimates of intervention effects, they are the ideal study type to answer intervention questions. However, not all RCT provide valid results. Validity of RCT depends on the underlying methodological quality (1). Allocation concealment, blinding, intention-to-treat analysis, and loss to follow-up are the critical items in the design and conduct of RCT, and inadequately conceived and conducted RCT, like observational studies, may overestimate or underestimate true effects of interventions (2-11).To our knowledge, there has never been a systematic evaluation of the number, coverage, and quality of RCT in nephrology. This was the aim of our study. If problems were identified, we also sought to propose feasible solutions. Materials and Methods Number and Proportion of RCT in Nephrology Compared with Other SpecialtiesThe medical subject heading (MESH) tree structure in MEDLINE (2002) was used to identify all major headings relevant to the primary specialties of internal medicine. Specifically, eight areas of internal medicine were searched by using the single broadest heading in the MeSH structure (cardiolog...

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“…Studies similar to ours have been conducted in other specialties (3,(21)(22)(23)(24). These also show problems in the conduct and design of trials in other specialties.…”

Section: Discussionmentioning

confidence: 83%

The Number, Quality, and Coverage of Randomized Controlled Trials in Nephrology

Strippoli

Craig²,

Schena³

2004

Journal of the American Society of Nephrology

294

200

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“…The lack of blinding on the part of the participating GPs would be likely to increase rather than decrease the chances of finding a significant eVect of the recommendation letter. 16 Although our definition of the GP known best to women was arbitrary, again it would be likely to increase the eVect of our intervention.…”

Section: Discussionmentioning

confidence: 99%

“…Thirdly, eVects of interventions may be overestimated through poor study design, in particular by failure to conceal the allocation during randomisation. 16 Our study benefited from stratification of prognostic factors aVecting mammography attendance and from concealment of allocation during randomisation. Only one of the 20 studies cited in the review 8 used prognostic stratification and one used a concurrent control group rather than randomisation design.…”

Section: Discussionmentioning

confidence: 99%

Can postal prompts from general practitioners improve the uptake of breast screening? A randomised controlled trial in one east London general practice

et al. 1998

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Objective-To determine the eVect on the uptake of breast screening of a personalised letter from the general practitioner recommending mammography, sent to coincide with an invitation from the NHS breast screening programme. Design-Randomised control trial with stratification of prognostic variables. Setting-A group practice in Hackney, east London. Subjects-473 women invited for breast screening by the City and East London Breast Screening Service. Outcome measure-Attendance for mammography. Results-All women in the randomised trial were followed up; 134 of 236 (57%) randomly allocated to receive the prompting letter attended for mammography compared with 120 of 234 (51%) controls. This diVerence was not significant ( 2 =1.43, p=0.23) Conclusion-Personal recommendation by a letter prompting attendance for mammography from the general practitioner known best to women due to be screened did not improve uptake of breast screening in this east London practice. Other strategies are needed to increase uptake of mammography in inner cities. (J Med Screen 1998;5:49-52) Keywords: breast cancer; general practitioners; patient compliance One in 12 women will develop breast cancer at some stage in their life.1 In an eVort to tackle this major public health problem, the National Health Service breast screening programme (NHSBSP) invites all women aged 50 to 64 for a mammogram every three years. Seventy per cent of women need to accept their invitations if the Health of the Nation target of a 25% reduction in breast cancer mortality by the year 2000 is to be achieved.2 3 Although nationally 71% of eligible women were screened in 1991-92, 4 a more recent review reports uptake rates of 77% in 1995.5 Uptake in inner cities has been low and uptake in City and East London Health Authority (Hackney, Tower Hamlets, and Newham) was 45% between 1989 and 1992.6 A more recent report gives uptake rates as low as 38% in this area. 7A systematic review of computer generated reminders for doctors and patients suggested that they probably increase the uptake for cancer screening services.8 However, few of the studies cited were randomised, and most were based in America, in "academic" rather than community settings. A small retrospective analysis in a Scottish general practice showed that personal knowledge of the general practitioner was positively related to attendance. 9 Defining simple interventions that can be used by inner city primary health care teams to increase mammography uptake may be crucial to the success of the NHSBSP. We used a randomised controlled trial to test the eVect on breast screening uptake rates of a personal letter prompting attendance for mammography from the general practitioner best known to each woman. MethodThe trial took place in an inner city training general practice in Hackney, east London, comprising seven principals with a list size of 11 194. The area has one of the highest levels of deprivation in the United Kingdom, and a large Turkish population. 10 In March 1996 the NHSBSP was conducting...

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“…36,37 Even in so-called double-blind trials, the outcome assessor may in fact not have been blind, particularly if the assessor was involved in the care of the patient and the treatment was associated with particular side effects. 38 It was usually impossible to determine from the reports which were the primary and secondary outcomes. More emphasis should be given to the results of the prespecified primary outcomes because these are the ones the trial was specifically designed to test.…”

Section: Discussionmentioning

confidence: 99%

Assessment of Clinical Outcomes in Acute Stroke Trials

Roberts

Counsell

1998

Stroke

133

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Background and Purpose-Adequate outcome assessment is crucial to randomized trials. We wished to assess the types of outcomes used in acute stroke trials and the appropriateness of these outcomes and their analyses. Methods-Acute stroke trials from the Cochrane Stroke Group's database were included from 1955 to 1995 if they were published in full text in English. For each trial we collected year of publication, number of patients randomized, blinding of outcome assessment, the specific outcome instruments used, the statistical methods used for analysis, and the significance of the results. The validity and reliability of each outcome measure were assessed by review of the literature. Results-Our study included 174 trials. Outcomes were assessed blindly in 69%. Death was recorded in only 76% of trials, impairment in 76%, disability in 42%, and handicap or quality of life in only 2%. Of the trials that measured impairment, 35% used a measure of established validity or reliability. For disability and handicap, the proportions with valid or reliable measures were 70% and 25%, respectively. Impairment and handicap measures were primarily analyzed as continuous variables, while disability was mainly analyzed as a dichotomous variable. Continuous data were usually analyzed with inappropriate parametric statistics. There was no relationship between the method of analysis, the type of outcome, and the statistical significance of results. Conclusions-Most

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Blinding and exclusions after allocation in randomised controlled trials: survey of published parallel group trials in obstetrics and gynaecology

Cited by 146 publications

References 19 publications

The Number, Quality, and Coverage of Randomized Controlled Trials in Nephrology

The Number, Quality, and Coverage of Randomized Controlled Trials in Nephrology

Can postal prompts from general practitioners improve the uptake of breast screening? A randomised controlled trial in one east London general practice

Assessment of Clinical Outcomes in Acute Stroke Trials

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