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Sample size estimation practices in research protocols submitted to Danish scientific ethics committees

a , a , b ,

Contemporary Clinical Trials Communications

Elsevier

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      Abstract

      Background

      Sample size in research projects is estimated before initiation of the study to minimise type 1 and type 2 error, while keeping the study's financial cost and subject enrolment to a minimum. This study investigates project-specific factors potentially associated with correct estimation of sample size in study protocols.

      Methods

      Examination of 189 non-commercially sponsored study protocols (84 randomised controlled trials (RCTs) and 105 non-RCT studies) submitted to the Scientific Ethics Committees of The Capitol Region of Denmark from 2013 to 2015.

      Results

      119 (63%) study protocols contained a sample size calculation, with a significantly higher rate of sample size calculations in RCT vs non-RCT study protocols (76% vs. 52%, p < 0.001). Significantly more intervention studies than non-intervention studies (69% vs 52%, p = 0.020), studies including blood samples compared to those without (69% vs. 55%, p = 0.045), studies funded by a foundation donation compared to those with no funding (68% vs. 49%, p = 0.040) performed sample size calculations. Further, increasing number of sick patients enrolled (p = 0.048) and newer studies (p = 0.032) were more likely to include a sample size calculation in the protocol.

      Conclusions

      Estimation of sample size is more often reported in RCT than non-RCT study protocols. Also, intervention studies, studies funded by a foundation donation, studies including blood samples, studies with a greater amount of sick participants and chronologically newer study protocols more often reported a sample size calculation.

      Related collections

      Most cited references 8

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      The size of a pilot study for a clinical trial should be calculated in relation to considerations of precision and efficiency.

      To investigate methods to determine the size of a pilot study to inform a power calculation for a randomized controlled trial (RCT) using an interval/ratio outcome measure. Calculations based on confidence intervals (CIs) for the sample standard deviation (SD). Based on CIs for the sample SD, methods are demonstrated whereby (1) the observed SD can be adjusted to secure the desired level of statistical power in the main study with a specified level of confidence; (2) the sample for the main study, if calculated using the observed SD, can be adjusted, again to obtain the desired level of statistical power in the main study; (3) the power of the main study can be calculated for the situation in which the SD in the pilot study proves to be an underestimate of the true SD; and (4) an "efficient" pilot size can be determined to minimize the combined size of the pilot and main RCT. Trialists should calculate the appropriate size of a pilot study, just as they should the size of the main RCT, taking into account the twin needs to demonstrate efficiency in terms of recruitment and to produce precise estimates of treatment effect. Copyright © 2012 Elsevier Inc. All rights reserved.
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        The continuing unethical conduct of underpowered clinical trials.

        Despite long-standing critiques of the conduct of underpowered clinical trials, the practice not only remains widespread, but also has garnered increasing support. Patients and healthy volunteers continue to participate in research that may be of limited clinical value, and authors recently have offered 2 related arguments to support the validity and value of underpowered clinical trials: that meta-analysis may "save" small studies by providing a means to combine the results with those of other similar studies to enable estimates of an intervention's efficacy, and that although small studies may not provide a good basis for testing hypotheses, they may provide valuable estimates of treatment effects using confidence intervals. In this article, we examine these arguments in light of the distinctive moral issues associated with the conduct of underpowered trials, the disclosures that are owed to potential participants in underpowered trials so they may make autonomous enrollment decisions, and the circumstances in which the prospects for future meta-analyses may justify individually underpowered trials. We conclude that underpowered trials are ethical in only 2 situations: small trials of interventions for rare diseases in which investigators document explicit plans for including their results with those of similar trials in a prospective meta-analysis, and early-phase trials in the development of drugs or devices, provided they are adequately powered for defined purposes other than randomized treatment comparisons. In both cases, investigators must inform prospective subjects that their participation may only indirectly contribute to future health care benefits.
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          Statistics and ethics in medical research: III How large a sample?

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            Author and article information

            Affiliations
            [a ]Department of Dermatology, Bispebjerg Hospital, Copenhagen, Denmark
            [b ]Department of Biomedical Sciences, University of Copenhagen, Copenhagen, Denmark
            Author notes
            []Corresponding author. Department of Dermatology, Bispebjerg Hospital, Bispebjerg Bakke 23, DK-2400, Copenhagen, NV, Denmark. simonfrancisthomsen@ 123456gmail.com
            Contributors
            Journal
            Contemp Clin Trials Commun
            Contemp Clin Trials Commun
            Contemporary Clinical Trials Communications
            Elsevier
            2451-8654
            15 August 2018
            September 2018
            15 August 2018
            : 11
            : 165-169
            6104346
            S2451-8654(18)30072-3
            10.1016/j.conctc.2018.08.003
            © 2018 The Authors

            This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

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