PLoS ONE (Jan 2022)

The importance of effect sizes when comparing cycle threshold values of SARS-CoV-2 variants.

  • Celine Brinkmann,
  • Peter Gohl,
  • Dietrich Mack,
  • Johannes Pfeifer,
  • Mònica Palmada Fenés,
  • Oliver Harzer,
  • Bernhard Zöllner

DOI
https://doi.org/10.1371/journal.pone.0271808
Journal volume & issue
Vol. 17, no. 7
p. e0271808

Abstract

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PurposeWe aimed to elaborate whether cycle threshold (Ct) values differ significantly between wild type SARS-CoV-2 (wtV) and certain viral variants and how strong or weak a potential significant effect might be.MethodsIn a retrospective study, we investigated 1873 SARS-CoV-2 positive samples for the occurrence of viral marker mutations. Age, gender, clinical setting, days after onset of symptoms, and Ct values were recorded. Statistical analysis was carried out with special consideration of effect sizes.ResultsDuring the study period wtV was detected in 1013 samples (54%), while 845 (45%) patients carried the Alpha variant of concern (VOC), and 15 (1%) the Beta VOC. For further analysis, only wtV and the Alpha VOC were included. In a multi-factor ANOVA and post-hoc test with Bonferroni-correction for the age groups we found significant main-effects for Ct values of the viral variant (wtV mean 26.4 (SD 4.27); Alpha VOC mean 25.0 (SD 3.84); F (1,1850) = 55.841; p ConclusionsIn order to compare different variants of SARS-CoV-2 the calculation of effect sizes seems to be necessary. A combination of p-values as estimates of the existance of an effect and effect sizes as estimates of the magnitude of a potential effect may allow a better insight into transmission mechanisms of SARS-CoV-2.