Distribution of log P for Z = 0.014 (left), 0.006 (middle), and 0.002 (right panel). The SYCLIST populations appear in red, while observations are shown as black histograms. Observations come from Pietrukowicz et al. (2021) and Soszyński et al. (2015, 2017) for Classical Cepheids in the Milky Way and Magellanic Clouds, respectively. Observational counts have been rescaled in order to match the numbers we have in SYCLIST simulations, by a factor 3.4, 5.9, and 7.5 for Z = 0.014, 0.006, and 0.002, respectively. The age limit applied (< 300 Myr) to the synthetic populations leads to mismatches at the shortest periods, particularly at Z = 0.002.