Selection Bias and Covariate Imbalances in Randomized Clinical Trials

Berger, Vance W.

doi:10.1002/0470863641

Cited by 216 publications

(288 citation statements)

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“…I distinguish the effort to mask from the success of the endeavor [1]. Given the nature of the treatments involved, it is unlikely that even the one study that claimed masking could have been truly masked, although de facto masking [2] is always an option, and probably should have been used to at least conceal which treatment was the active one.…”

Section: To the Editormentioning

confidence: 99%

“…Given the nature of the treatments involved, it is unlikely that even the one study that claimed masking could have been truly masked, although de facto masking [2] is always an option, and probably should have been used to at least conceal which treatment was the active one. Therefore with or without the claim of masking, none of the studies can be taken as perfectly masked, and any unmasking at all, coupled with any form of restricted randomization (such as permuted blocks), precludes the possibility of allocation concealment, because knowledge of even some of the prior allocations can allow for prediction of future ones [1,4]. Unless the trials used unrestricted randomization, which almost no trials use in practice, there was no allocation concealment.…”

Section: To the Editormentioning

confidence: 99%

“…Unless the trials used unrestricted randomization, which almost no trials use in practice, there was no allocation concealment. This does not imply that the randomization was improper, as there are also drawbacks to using unrestricted randomization [1,4]. However, the use of an excessively restricted procedure, such as permuted blocks, is inappropriate when masking is uncertain.…”

Section: To the Editormentioning

confidence: 99%

“…However, the use of an excessively restricted procedure, such as permuted blocks, is inappropriate when masking is uncertain. Grimm et al should have displayed in Table 2 the specific randomization procedure used in each trial, but without this, we cannot assume that all 10 research teams knew to use minimally restrictive procedures such as the (paradoxically named, given its introduction here) maximal procedure [1,4].…”

Section: To the Editormentioning

confidence: 99%

See 3 more Smart Citations

Letter to the Editor: Efficacy and Degree of Bias in Knee Injury Prevention Studies: A Systematic Review of RCTs

Berger

2013

Clinical Orthopaedics &Amp; Related Research

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Section: To the Editormentioning

confidence: 99%

Section: To the Editormentioning

confidence: 99%

Section: To the Editormentioning

confidence: 99%

Section: To the Editormentioning

confidence: 99%

See 2 more Smart Citations

Letter to the Editor: Efficacy and Degree of Bias in Knee Injury Prevention Studies: A Systematic Review of RCTs

Berger

2013

Clinical Orthopaedics &Amp; Related Research

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“…14,15 Since 2005, Berger et al advocate the inclusion of tests into the methodology of RCTs that provide empirical evidence as to whether randomisation and allocation concealment were indeed effective in protecting against selection bias. [13][14][15] We believe that only the reporting of such evidence merits the judgement of a trial as being of 'low selection bias risk'. According to such a rather stringent standard, we agree with Dr Hurst that all of our appraised evidence is to be regarded as 'poor'.…”

Section: Letters To Ebd Letters Wwwnaturecom/ebdmentioning

confidence: 99%

Letters to EBD

Mickenautsch

Yengopal

Perry³

2012

Evid Based Dent

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Re: Commentary: Poor quality evidence suggests that failure rates for atraumatic restorative treatment and conventional amalgam are similar.Evid Based Dent 2012; 13: 46-47. Dear SirWe would like to thank Dr Dominic Hurst for reading our systematic review update. 1 However, most of his criticism of our article seems unnecessary. 2 His objections to the appraisal of evidence regarding the question as to whether the placement of an ART (atraumatic restorative treatment) or a conventional amalgam filling would yield lesser, same or higher chance of failure appears to be underlined by the opinion that ART may not be relevant for modern dental settings. This is an unfortunate misconception. 3 Of course, other questions to the clinical merits of ART are important, too, and we look forward to learn of the findings of Dr Hurst's own two, still ongoing systematic reviews to the topic. 4,5 Dr Hurst is correct in his assumption that we did not know about the five Chinese medical databases. 6 We would like to thank him for pointing this out and will focus on it in our next systematic review update. However, the concept of language bias needs to be regarded within the context that the exclusion of non-English trials may have little effect on summary treatment effect estimates. 7,8 The results of all non-English trials (including the Chinese trials) in our review update seem to confirm this. 9 Some further points of criticism raised by Dr Hurst are: the question as to which literature source our identified Chinese trials originate from (but we made all literature sources explicit in Tables 6 and 7, as well as in the text); the question to why 'ART' [MeSH] as a search term was used (but it can be discerned from our Table 4 that this was the first and broadest search term (#1), which then got narrowed down to the final search term #6 resulting in 260 hits); his confusion regarding the randomisation status of accepted trials (but this is presented in our Table 14 on hand of all verbatim quotes extracted from the text of accepted trials that had relevance to selection-, performance-and detection bias risk); lack of summary of the included trials (but important characteristic of trials are presented in Tables 8-10); the impression that more evidence is given for primary than for permanent teeth (but our Table 13 rather indicates a higher number of evidence relevant to permanent teeth in terms of measured outcomes and number of subjects); the questioning of the 'usefulness' of grouping 'restorations evaluated according to USPHS criteria after 1 year' if type of dentition nor restoration class was specified (yes, 'usefulness' is indeed limited when important information are not reported in trials, but a pooled effect estimate -aspects of heterogeneity allowing -represent available evidence better than a number of individual ones).In addition, when reading through the PRISMA checklist 10 it is difficult to understand which section we may have missed. Indeed, our review report is rather complex but this is due to the detail...

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Block Randomization

McEntegart¹

2005

Encyclopedia of Statistical Sciences

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Simple unconstrained randomization is the yardstick for randomization techniques in clinical trials as it is completely unpredictable and provides an unambiguous basis for inference from statistical analysis. But simple randomization is rarely used because of the need to protect the trial from imbalance in the overall numbers allocated to treatment and from temporal bias in the allocations. For these reasons the randomization procedure is often restricted by some form of blocking, the most common being random permuted blocks. The methodology, issues and practical considerations relating to the use of blocked randomization are described. Particular attention is paid to the issue of potential selection bias, which may arise from the predictability of tail allocations towards the end of any block of treatment allocations if the past allocations in the block are known or can be guessed. The merits of using unequally sized blocks to avoid selection bias are discussed in detail. Inference following blocked randomization is also discussed. Alternative forms of blocking are described; these include lists generated from the maximal procedure, the use of rows from Hadamard matrices, Zelen's balanced blocks procedure and mixed randomization. Practical considerations relating to the use of blocked randomization are described including software used to generate random blocks. Also covered are considerations relating to the use of electronic systems to automatically perform allocation from a pre‐defined randomization list; the use of such systems is becoming increasingly common with the advent of telephone interactive voice response (IVR) and web based randomization systems.

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Selection Bias and Covariate Imbalances in Randomized Clinical Trials

Cited by 216 publications

References 0 publications

Letter to the Editor: Efficacy and Degree of Bias in Knee Injury Prevention Studies: A Systematic Review of RCTs

Letter to the Editor: Efficacy and Degree of Bias in Knee Injury Prevention Studies: A Systematic Review of RCTs

Letters to EBD

Block Randomization

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