Data obtained in situations in which the act of measurement does not affect the behavior of the object that is measured. For example, to forecast sales in shopping malls, one could secretly count the number of cars in the parking lots at various times, perhaps using photographs from high locations. The shoppers do not know they are being counted. Awareness of the measurement can change people’s behavior. Fitzsimons and Morwitz (1996) present evidence 
 that the use of <a href="search.pl?p=intentions surveys">intentions surveys</a> can affect subsequent behavior. <o:p></o:p></P>
 <ul>
   <li>Fitzsimons, G. &amp; V. G. Morwitz (1996), “The effect 
of measuring intent on brand-level purchase behavior,” <I>Journal of Consumer 
Research</I>, 23, 1-11.</li>
 </ul>