it's the ratio of new cases to total, which accounts for the comparability. most countries remain comparable with themselves, and those that do change method, s

it's the ratio of new cases to total, which accounts for the comparability. most countries remain comparable with themselves, and those that do change method, since the growth is exponential, it tends to drown out any incomparabilities quickly enough. anyway, the proof is in the pudding. the data isn't smushed to the point of making individual variability invisible