Thus, whereas the ideal of measurement is for all items of a test to measure the same latent variable, alpha has been demonstrated many times to attain quite high values even when the set of items measures several unrelated latent variables.[5][6][7][8][9][10][11] The hierarchical "coefficient omega" may be a more appropriate index of the extent to which all of the items in a test measure the same latent variable.[12][13] Several different measures of internal consistency are reviewed by Revelle & Zinbarg (2009).[14][15]