Sensitivity and Appropriateness:

Sensitivity  refers  to  the capability  to  detect  changes or differences when they to occur. Often, multimodel measurements  are made because of variations in sensitivity e.g.  some  fear-reduction research has shown that changes  in subjective feelings are not necessarily accompanied  by  changes  in elevated heart  rate. Heart rate, therefore, may  not be  sensitive  enough  to demonstrate change as  a result  of some interventions  particularly  if  it is  observed immediately after administration of the experimental variable. Therefore, it  is necessary to include different 'measures to estimate  fear. 

Appropriateness refers  to whether  or not the measure can be  used for a particular target population. It also refers  to  the extent  to which the target population can meet demands of the instrument, such as understanding and following the directions and having the physical stamina and motivation  to complete the measure.  If  a measure is inappropriate it could measure wrongly.