The study by Doudin et al. [2], exploring the association between serum 25(OH)D and hematological indices in adolescents, stands out for the wise use of cross-sectional data from a German cohort to explore a novel issue related to vitamin D.

The authors’ interpretation of the findings is misled by the use of p value. Applying it to assess associations whose underlying plausibility is ignored and is not suggested by the correlation coefficients, easily leads to false-positive findings. In fact, p values are strongly related to sample size [6], “sometimes attracting attention to very small effects that have little real-world importance” [1].

The authors acknowledge that “the correlation coefficients and the effect sizes are very small” [2]. Indeed, the correlation coefficient estimates range from r = −0.04 to r = 0.08 (very close to r = 0, i.e., absence of correlation), and the differences on hematological indices by levels of serum 25(OH)D are minimal (e.g., Hb [g/dl] 1st tertile: 13.7 ± 1.2; 2nd tertile: 13.5 ± 1.1; 3rd tertile 13.6 ± 1.1), in spite of the low estimated p values. None of the “statistically significant” differences found have a clear “clinical relevance” [3].

This frequent methodological error prompted methodologists and editors to discourage the widespread use of p values and to promote the use of alternative measures, with scarce success [4]. “False positive findings are detrimental to science and society, as once published, they accumulate persistent untrue evidence” [5].