I have a theory that the oldest (or only) child is the most dissociative. Younger siblings are more likely to attempt suicide (I had this theory for a while, and just googled it and realized this is a Thing). I think, when things get tough, the oldest sibling is more likely to "kill" themself by dissociating, but the younger siblings feel more free to act out and actually try to kill themselves.
I've noticed this pattern with friends, me & my sibling, my dad and his siblings...actually, I don't know anyone who's attempted suicide who was the oldest child.
It seems that the oldest child usually performs better at school (because they feel like they have to), are more responsible (because they feel like they have to be), and feel like they must soldier on/suck it up/power through life, whereas the younger siblings might do worse at school but imo are a bit better off emotionally because they don't have as much pressure put on them... So they also feel more free to do something like attempt suicide, whereas the oldest wouldn't feel like they weren't "allowed" to do something like that because they have to be "strong" and responsible or whatever. They would be less likely to see suicide as an "option." I'm sure I'm rambling, but just curious to see the results of this poll.