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Geometric Mean IELT and Premature Ejaculation: Appropriate Statistics to Avoid Overestimation of Treatment Efficacy

Authors

  • Marcel D. Waldinger MD, PhD,

    Corresponding author
    1. Department of Psychiatry and Neurosexology, Haga Hospital Leyenburg, The Hague, The Netherlands;
    2. Department of Psychopharmacology, Utrecht Institute for Pharmaceutical Sciences and Rudolf Magnus Institute for Neurosciences, Faculty of Pharmaceutical Sciences, Utrecht University, Utrecht, The Netherlands;
      Marcel D. Waldinger, MD, PhD, Department of Psychiatry and Neurosexology, HagaHospital Leyenburg, Leyweg 275, The Hague, The Netherlands. Tel: +31-70-2102086; Fax: +31-70-2104902; E-mail: md@waldinger.demon.nl
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  • Aeilko H. Zwinderman PhD,

    1. Department of Medical Statistics, Clinical Epidemiology and Biostatistics, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands;
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  • Berend Olivier PhD,

    1. Department of Psychopharmacology, Utrecht Institute for Pharmaceutical Sciences and Rudolf Magnus Institute for Neurosciences, Faculty of Pharmaceutical Sciences, Utrecht University, Utrecht, The Netherlands;
    2. Department of Psychiatry, Yale University School of Medicine, New Haven, CT, USA;
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  • Dave H. Schweitzer MD, PhD

    1. Department of Internal Medicine and Endocrinology, Reinier de Graaf Groep Hospital, Delft-Voorburg, The Netherlands
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Marcel D. Waldinger, MD, PhD, Department of Psychiatry and Neurosexology, HagaHospital Leyenburg, Leyweg 275, The Hague, The Netherlands. Tel: +31-70-2102086; Fax: +31-70-2104902; E-mail: md@waldinger.demon.nl

ABSTRACT

Introduction.  The intravaginal ejaculation latency time (IELT) behaves in a skewed manner and needs the appropriate statistics for correct interpretation of treatment results.

Aims.  To explain the rightful use of geometrical mean IELT values and the fold increase of the geometric mean IELT because of the positively skewed IELT distribution.

Methods.  Linking theoretical arguments to the outcome of several selective serotonin reuptake inhibitor and modern antidepressant study results.

Main Outcome Measures.  Geometric mean IELT and fold increase of geometrical mean IELT.

Results.  Log-transforming each separate IELT measurement of each individual man is the basis for the calculation of the geometric mean IELT. A drug-induced positively skewed IELT distribution necessitates the calculation of the geometric mean IELTs at baseline and during drug treatment. In a positively skewed IELT distribution, the use of the “arithmetic” mean IELT risks an overestimation of the drug-induced ejaculation delay as the mean IELT is always higher than the geometric mean IELT. Strong ejaculation-delaying drugs give rise to a strong positively skewed IELT distribution, whereas weak ejaculation-delaying drugs give rise to (much) less skewed IELT distributions. Ejaculation delay is expressed in fold increase of the geometric mean IELT.

Conclusions.  Drug-induced ejaculatory performance discloses a positively skewed IELT distribution, requiring the use of the geometric mean IELT and the fold increase of the geometric mean IELT. Waldinger MD, Zwinderman AH, Olivier B, and Schweitzer DH. Geometric mean IELT and premature ejaculation: Appropriate statistics to avoid overestimation of treatment efficacy. J Sex Med 2008;5:492–499.

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