$Q(\theta | \theta^{(t)}) = E_{\theta^{(t)}} [\log L(\theta; X, Z) | X]$

$Q(\theta | \theta^{(t)}) = E_{\theta} [\log L(\theta^{(t)}; X, Z) | X]$

$Q(\theta | \theta^{(t)}) = \sum P(Z|X, \theta^{(t)})$

$Q(\theta | \theta^{(t)}) = L(\theta; X) / L(\theta^{(t)}; X)$