How do you decide on EVs for a defensive pokemon?

Question

For example with an Electric pokemon its only weakness is Ground, which 99% of the time means Earthquake and physical damage. Therefore Special Defense isn't as important here.

But how would you decide for other types? Psychic's weaknesses are Bug/Ghost/Dark - is special or physical damage more likely to come your way? Or would it be equal? And are there other things to take into account?

Answer 1

I go mainly by the type of the pokemon that will try to counter it. For instance, If my team has a ghost weakness, I know I have to be ready for that. Gengar is probably the most common and powerful ghost type around.
I prepare against him by investing EVs in special defense because that is going to be my likely counter. That isn't the only way of choosing EVs by any means though, there are other ways you could think through it.

Answer 2

If there is a greater amount of Special majority type weaknesses (Fire, Water, Electric, Grass, Ice, Poison, Psychic, Ghost) then I go with Sp Def (poison due to Sludge Bomb being a common Poison type move.) If there is a greater amount of physical weaknesses (Fighting, Ground, Flying, Bug, Rock, Dragon, Dark, Steel) then I choose Defense. If there is an equal amount of weaknesses on both sides, I go with HP. However, I give EVs to the stats with the highest base, because usually it is close to useless making for example Speed go up from the high 100s to the low 200s because most Pokemon would still be able to outspeed the Pokemon.