$I(\theta) = -E[\frac{\partial^2}{\partial \theta^2} \ell(\theta)]$

$I(\theta) = E[\frac{\partial}{\partial \theta} \ell(\theta)]$

$I(\theta) = \frac{\partial^2}{\partial \theta^2} \ell(\theta)$

$I(\theta) = Var(\ell(\theta))$