BERLIN — Russia’s military made its largest territorial gains in more than two years in October, as it pressed farther into Ukraine’s eastern Donbas region — but at a heavy cost.

British and Ukrainian military officials, as well as BBC researchers, claim that Russia suffered its highest rate of dead and injured soldiers during that month. The arrival of thousands of North Korean troops in Russia is also raising questions about whether the Kremlin has enough soldiers to make up for its losses.

What do we really know about Russia’s casualties and its ability to replace them?

The losse

It is difficult to obtain concrete information about Russian casualties, which comprise deaths and injuries. Moscow has an incentive to minimize its losses and rarely discloses any information; Ukraine and its allies have an incentive to overstate them.

Even if they are accurate, the Western casualty estimates usually lump together deaths with all injuries. Military experts say that category is too broad to fully explain the state of the war. Lightly wounded soldiers can quickly recover, for example.

What determines a military’s true ability to fight are its irreplaceable, irrecoverable or permanent losses — soldiers who are dead or so seriously injured that they will never see battle again.

Russia and Ukraine treat such statistics as state secrets.

Ukraine guards its casualty figures especially closely, restricting journalists’ ability to report on the topic, withholding information from allies and halting the publication of demographic data.

Some independent Russian journalists and researchers have found innovative ways to count Russia’s dead and wounded, digging up information from diverse sources like obituaries, cemeteries, disability payments and notary databases.

Their calculations begin to show a more accurate toll of the war, shedding light on Russia’s ability to continue the fight. They also suggest that Russia has lost more soldiers in this war than any industrialized nation has in a conflict since World War II.

The dead

Journalists from the independent Russian news outlet Mediazona and the BBC Russian Service have been counting Russian soldiers who have died in Ukraine since the early months of the invasion. Their methods are based on collecting and cross-checking public information such as obituaries and cemetery burials.

This work has produced the most comprehensive database of confirmed Russian combat deaths: 78,000 soldiers by November, not including the Ukrainian separatists and foreigners fighting for Russia. (A similar, but less transparent, account of Ukraine’s losses found 65,000 dead soldiers by mid-November.)

Mediazona’s tally is incomplete.

inheritances

Another independent Russian news outlet, Meduza, collaborated with Mediazona and the BBC for a statistical analysis of war casualties.

Their main tool is Russia’s public notary database, which contains all inheritance cases opened by the relatives of killed soldiers. To collect the data, Meduza and Mediazona journalists must outsmart government programmers who try to block them from locating and downloading inheritance entries.

Once the data is collected, the journalists use statistical tools.

This analysis of excess mortality led the journalists to estimate Russia’s total military deaths at nearly 150,000 by the end of October.