This chapter reviewed the nature of reactivity, changes that come about in a target due to the act of measurement. We discussed different sources of reactivity, and we suggested a number of ways of...

This chapter reviewed the nature of reactivity, changes that come about in a target due to the act of measurement. We discussed different sources of reactivity, and we suggested a number of ways of overcoming reactivity in general. We then focused on reactivity in self-monitoring and offered several guidelines for how to increase or decrease reactivity depending upon what is desirable in a given case. The remainder of the chapter dealt with unobtrusive measures. Unobtrusive measures are measures that can be used to evaluate changes over time without interfering with or affecting the observed target simply by the act of measurement. In large part, these measures are most suited as secondary sources of data, although in certain instances, where they comprise direct evidence of changes, they may be suitable as primary measures. Four types of unobtrusive measures were described and examples presented of their potential use for practice: archival records (both public and private), physical traces (evidence left behind by the client), behavior products (rather than the actual behaviors themselves), and unobtrusive observations, where the observer doesn’t play an active part in the client’s interactions on the dimension being observed.