What this is
If Pokémon's ratings had fallen for Pokémon-specific reasons the ratio to Doraemon would fall; it is flat on listed weeks (0.44 -> 0.45) and rises on the upper bound (0.44 -> 0.55). Doraemon, whose rating fell in the same proportion, stayed 1st-2nd with children in every survey here.
Where it comes from
Our calculation from other figures in the trainer’s notes: