Characterization of entanglement of more than two qubits with Bell   inequalities and global entanglement
  It is shown that the entanglement-structure of 3- and 4-qubit states can be characterized by optimized operators of the Mermin-Klyshko type. It is possible to discriminate between pure 2-qubit entanglements and higher entanglements. A comparison with a global entanglement measure and the i-concurrence is made. 
J. Endrejat, H. Buettner