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Comparison against baseline in randomised control trials (again)

Sérvulo Azevedo Dias-Júnior, Rafael Stelmach, Regina Maria de Carvalho-Pinto, Alberto Cukier
European Respiratory Journal 2014 44: 1376-1377; DOI: 10.1183/09031936.00117314
Sérvulo Azevedo Dias-Júnior
Pulmonary Division, Heart Institute (InCor), Hospital das Clínicas da Faculdade de Medicina da Universidade de São Paulo, São Paulo, Brazil
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Rafael Stelmach
Pulmonary Division, Heart Institute (InCor), Hospital das Clínicas da Faculdade de Medicina da Universidade de São Paulo, São Paulo, Brazil
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Regina Maria de Carvalho-Pinto
Pulmonary Division, Heart Institute (InCor), Hospital das Clínicas da Faculdade de Medicina da Universidade de São Paulo, São Paulo, Brazil
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Alberto Cukier
Pulmonary Division, Heart Institute (InCor), Hospital das Clínicas da Faculdade de Medicina da Universidade de São Paulo, São Paulo, Brazil
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  • For correspondence: pnealberto@incor.usp.br
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From the authors:

We thank J.D. Blakey for his interest in our article [1]. In the paper he cited, Bland and Altman [2] criticise randomised studies in which baseline is compared with a final measurement separately for each group through paired t-tests. By using simulations, they concluded that the use of paired tests against baseline separately for each group is conceptually wrong and statistically invalid. We agree that this is not a proper approach. However, this was not the approach adopted in our study. As explained in the Methods section, we applied a repeated-measures ANOVA that allows integration of the between- and within-group analyses into the same model. This methodology starts from the hypothesis of interaction between group and time; a significant p-value for this hypothesis indicates that groups behave differently across time, and, in this situation, the within-group comparisons should be performed directly in this model as contrasts. Therefore, the methodology adopted in our study was, indeed, different from the one criticised by Bland and Altman [2], and we assure you that we used a statistically valid method [3, 4].

Acknowledgments

The authors thank C.S. Redigolo (Dept of Public Politics and Public Health, Federal University of São Paulo, Santos, Brazil) and R.A. de Oliveira Figueiredo (Faculty of Public Health, University of São Paulo, São Paulo, Brazil) for assistance with the statistical analysis.

Footnotes

  • Conflict of interest: Disclosures can be found alongside the online version of this article at erj.ersjournals.com

  • Received June 26, 2014.
  • Accepted June 30, 2014.
  • ©ERS 2014

References

  1. ↵
    1. Dias-Júnior SA,
    2. Reis M,
    3. de Carvalho-Pinto RM,
    4. et al
    . Effects of weight loss on asthma control in obese patients with severe asthma. Eur Respir J 2014; 43: 1368–1377.
    OpenUrlAbstract/FREE Full Text
  2. ↵
    1. Bland JM,
    2. Altman DG
    . Comparisons against baseline within randomised groups are often used and can be highly misleading. Trials 2011; 12: 264.
    OpenUrlCrossRefPubMed
  3. ↵
    1. Diggle PJ,
    2. Heagerty PJ,
    3. Liang K,
    4. et al
    . Analysis of Longitudinal Data. 2nd Edn. Oxford, Oxford Science Publications, 2002.
  4. ↵
    1. Chow S,
    2. Liu J
    . Design and analysis of clinical trials: concepts and methodologies. 3rd Edn. New York, John Wiley & Sons Inc., 2014.
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Comparison against baseline in randomised control trials (again)
Sérvulo Azevedo Dias-Júnior, Rafael Stelmach, Regina Maria de Carvalho-Pinto, Alberto Cukier
European Respiratory Journal Nov 2014, 44 (5) 1376-1377; DOI: 10.1183/09031936.00117314

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Comparison against baseline in randomised control trials (again)
Sérvulo Azevedo Dias-Júnior, Rafael Stelmach, Regina Maria de Carvalho-Pinto, Alberto Cukier
European Respiratory Journal Nov 2014, 44 (5) 1376-1377; DOI: 10.1183/09031936.00117314
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