Will someone help explain to me how troop losses are calculated?

Is it a base % of the amount of troops sent vs troops defending? Anyone know the formula?

Also how do the racial factors affect the base % of troop loss?

For example an Orc/cleric

Orc has +10% casualties
Cleric has -35% casualties

Then hospitals have -10% casualties

Whats the final casualty %? Are they additive or multiplicative?

Thank you for your insights!