Why is there a difference in range between countries for the number of military deaths in World War I?

Earlier, I was reading this AskReddit question in which this answer came up.

More french soldiers died during WW1 than american soldiers during the entire US military history, including both sides of the civil war. The same can be said for Germany, Russia and Austria-Hungary. Yep, that's how much of a bloodbath the first world war was.

Death from World War I :

France : 1 357 000 to 1 397 800

Russian Empire : 1 700 000 to 2 254 369 (from 1914 to 1917)

German Empire : 1 773 700 to 2 037 000

Austria-Hungary : 1 200 000 to 1 494 200

United Kingdom : 735 204 to 1 590 628

American military deaths from 1775 to 2015 : 1 354 664

Is there any specific reason for why, say, France has a range of 40,000 possible deaths while Russia has a range of 500,000?