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Did the 2015 Lancet study differentiate flaccid stretched length from erect length and how?
Executive Summary
The 2015 systematic review by Veale et al. distinguished flaccid stretched length from erect length, reporting separate nomograms and mean values that are very close—flaccid stretched length around 13.2 cm and erect length around 13.1 cm—while also flagging methodological limits in erect measurements and inter-study variability [1] [2] [3]. Independent analyses and related studies show divergent single-study findings—some report lower flaccid means (≈9.2 cm) and other clinical work documents substantial underestimation when using stretched flaccid measures versus true erect length—highlighting measurement-method differences and sampling issues that shape reported averages [4] [5].
1. Why the paper’s headline numbers look the same but measurement methods matter
The Veale et al. review explicitly constructed separate nomograms for flaccid stretched length and erect length, and reported mean values that appear very similar: a flaccid stretched mean near 13.24 cm and an erect mean near 13.12 cm [1] [2]. These close means can obscure an important methodological point: flaccid stretched length is a manipulated measurement (the penis is extended maximally while flaccid), whereas erect length is measured during an erection, and the two methods capture different physiological states. The review also cautioned about the limited number of clinical erect measurements aggregated from diverse studies, meaning pooled averages may reflect different measurement contexts and protocols rather than a strict biological equivalence [1]. This distinction is central to interpreting why stretched and erect averages can converge in meta-analysis despite differing measurement biases.
2. Conflicting single-study data that complicates the picture
Some data aggregated in the review and in parallel summaries report notably different flaccid means—for example, a pooled flaccid mean of about 9.16 cm appears in one analysis of the same literature [4]. This divergence indicates heterogeneity across studies in participant samples, measurement technique, and reporting. The Veale review attempted to harmonize disparate studies into nomograms, but aggregation cannot fully eliminate biases introduced by inconsistent protocols—for instance, whether flaccid lengths were measured with firm traction, ambient temperature, observer training, or participant selection. The presence of both 13+ cm and ~9 cm flaccid estimates in analyses of the same literature underscores how sensitive average values are to inclusion criteria and measurement definitions [4] [3].
3. Clinical research shows stretched flaccid can misestimate erect length
Independent clinical research on interobserver variability and direct comparisons found that stretched flaccid measurements can substantially underestimate true erect length, with one study noting a mean underestimation of about 2.64 cm (21.4%) and significant variability between observers [5]. That finding challenges the simple interchangeability of stretched and erect measures: even if a systematic review yields similar means overall, at the individual or clinical level stretched measures may not reliably predict erect size. Interobserver variability further implies that without standardized training and protocols, measurements will vary—affecting both single-center studies and meta-analyses that pool heterogeneous data [5].
4. How the review handled heterogeneity and what it omitted
Veale et al. built nomograms by pooling studies with different measurement practices, and they acknowledged limitations: few studies measured erect length in clinical settings and there was variability across studies in how stretched flaccid length was obtained [1]. The review’s treatment of erect versus stretched endpoints is methodologically sound in that it separates the outcomes, but the pooled means must be read alongside the study-level heterogeneity. Observed discrepancies across secondary analyses [4] [3] reflect choices about which studies to include and how to treat outliers; those choices can shift reported population means substantially. The review did not eliminate the need for standardized, prospective measurement protocols to settle clinical-level predictiveness.
5. Bottom line: same labels, different implications for clinicians and researchers
The 2015 review did differentiate flaccid stretched from erect length and published nomograms for both, but the similarity of pooled mean values should not be taken to mean the two measures are interchangeable in practice [1] [2]. Conflicting pooled estimates and clinical studies showing underestimation by stretched measures highlight the importance of measurement context, observer training, and sample selection [4] [5]. For clinicians and researchers, the takeaway is that measurement method matters more than headline averages: use standardized protocols and interpret nomograms while keeping study heterogeneity and measurement bias front and center [1] [5].