Cumulative distributions of the physical diameter (top panel) and the spectral index α_{4–8 GHz} (bottom panel) for the Top7 (blue) and variable UC H II regions (red) of this work, and for the UC H II regions (black) from the GLOSTAR (Yang et al. 2023) or CORNISH (Kalcheva et al. 2018). A total of 32 of the 38 variable UC H II regions have their distances measured in Urquhart et al. (2018). The magenta line indicates diam=0.05 pc, i.e., the size criterion of the HC H II regions. This indicates that 100% of variable sources in this study meet the size criterion of HC H II regions. As the uncertainty in spectral index σ_α is large for weak sources in GLOSTAR (Yang et al. 2023), we limit the sources with σ_α < 0.1 here for α comparison.