Parallel studies should investigate mental processes that occur outside settings created by an investigator. It will usually be necessary to examine retrospective accounts of judgment made previously, learning about earlier processes as recalled by research participants. In general terms, the desirable research strategy is one that combines both idiographic and nomothetic approaches, encouraging people to identify the judgment and comparison but indexing those in standard terms for all participants (Enmons, 1986).
The mental processes considered here are likely often to extend or be repeated across times. Although most research in the area of this book has involved a single occasion of measurement, the study of happiness-relevant judgments and their activation could particularly benefit from exploration across an extended period. Longitudinal studies in this area could valuably focus on causal direction and seek to exclude possible third-variable interpretations. Experience-sampling procedures have considerable potential in that respect, taking a within-person (rather than the usual between-person) perspective across time (e.g., Fisher & Noble, 2004). In addition, longitudinal research of a qualitative kind is needed, using observation and/or repeated interview to explore patterns of thinking, types of comparators in each judgment category, and possible links between those categories.