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There are five main defense stats on your ship
Effective Hit Points is your health pool after resists are calculated into effect. Active Defenses is the amount of health you restore per second through one of the four drop down rates options you chose. Shields, Armor, and Structure are raw numbers that show the true health of the respective levels. It is important to note that resists do NOT factor into your true health numbers, ONLY your Effective Hit Points.
This wouldn't be Eve if we couldn't change all the stats of our ship and our opponent's, and we have quite a few options
EHP can be changed by adding any type of defense module on your ship that increases Resists or adds raw health. There are many Ship Modules that increase your EHP.
To calculate your ships EHP (which Eve does automatically for you) you take the resists for one type of health, average them and follow the formula below
Active Defenses are how much your ship is actively repairing itself in one second. There are four options in the drop down menu on the Fitting screen to see your Active Defenses for each defense type: