A final challenge for future research is to examine how models of successful aging may be useful for empirical research. The operationalization of processes is often difficult. For example, the concept of proactive coping embraces a process over time, which yet alone consists of many different elements, both behavioral strategies and cognitive activities, that cannot be determined in one single measurement. It would be useful to focus research on the smaller parts of the process using measurement instruments that do not depend on self-report. Self-report measures frequently include prepared response items that more often assess attitudes and dispositional acting styles instead of behavior that may change over time and may depend on the situation. Other problems include the fact that individuals are not able to report their efforts correctly (Schwartz, Neale, Marco, Shiffman, & Stone, 1999) and tend to employ socially desirable answering (Coyne & Gottlieb,1996). It might therefore be productive for future research to consider developing new measures.