The reference class is things you can be, i.e. things with subjective experience. This doesn’t actually make answering the question any easier, though it does mean it has other implications. Also, a smaller reference class is more likely (hence, doomsday), so that suggests that fewer creatures are sentient, and if possible, they’re sentient to a lesser degree, than we’d otherwise believe.
The reference class is things you can be, i.e. things with subjective experience. This doesn’t actually make answering the question any easier, though it does mean it has other implications. Also, a smaller reference class is more likely (hence, doomsday), so that suggests that fewer creatures are sentient, and if possible, they’re sentient to a lesser degree, than we’d otherwise believe.