Does ObservableCollection.RemoveAt() do two selections?

I have one doubt. You recomend me to use selectedItem instead of SelectedIndex, but when I do:

myObservableCollection.Remove(myItem);

Does this action a complex of O(n)? Because I have to iterate the collection until I get the ítem. However, if I use RemoveAt(), the complex is O(1).

Is that true?

Thank so much.