When Group Means Fail: Can One Size Fit All?

Abstract

The present study examined whether a cognitive process model that is inferred based on group data holds, and is meaningful, at the level of the individual person. Investigation of this issue is tantamount to questioning that the same set and configuration of cognitive processes is present within all individuals, a usually untested assumption in standard group-based experiments. Search from memory as assessed with the Sternberg memory scanning paradigm is among the most widely studied phenomena in cognitive psychology. According to the original memory scanning model, search is serial and exhaustive. Here we critically examined the validity of this model across individuals and practice. 32 younger adults completed 1488 trials of the Sternberg task distributed over eight sessions. In the first session, group data followed the pattern predicted by the original model, replicating earlier findings. However, data from the first session were not sufficiently reliable for identifying whether each individual complied with the serial exhaustive search model. In sessions six to eight, when participants performed near asymptotic levels of performance, between-person differences were reliable, group data deviated substantially from the original memory search model, and the model fit only 13 of the 32 participants' data. Our findings challenge the proposition that one general memory search process exists within a group of healthy younger adults, and questions the testability of this proposition at the individual level in single-session experiments. Implications for cognitive psychology and cognitive neuroscience are discussed with reference to earlier work emphasizing the explicit consideration of potentially existent individual differences.

Understanding the interplay of sleep and aging: Methodological challenges

“…We suggest that the basis for research on age‐dependent differences in a given (neural) process is rooted in thorough theoretical considerations that incorporate the complex and dynamic nature of aging (e.g., Cabeza et al, ; Cabeza, Nyberg, & Park, ; Lindenberger, Li, & Bäckman, ) and the individual as the primary unit of analysis (Fisher, Medaglia, & Jeronimus, ; Grandy, Lindenberger, & Werkle‐Bergner, ; Molenaar & Campbell, ; Nesselroade, Gerstorf, Hardy, & Ram, ; Nesselroade & Molenaar, ; Rose, Rouhani, & Fischer, ). Ideally, such a research process starts out with an exact definition of a neural or physiological phenomenon that we intend to investigate.…”

Understanding the interplay of sleep and aging: Methodological challenges

“…We suggest that the basis for research on age-dependent differences in a given (neural) process is rooted in thorough theoretical considerations that incorporate the complex and dynamic nature of aging (e.g., Cabeza et al, 2018Cabeza et al, , 2005Lindenberger et al, 2006) and the individual as the primary unit of analysis (Fisher et al, 2018;Grandy et al, 2017;Molenaar and Campbell, 2009;Nesselroade et al, 2007;Nesselroade and Molenaar, 2016;Rose et al, 2013). Ideally, such a research process starts out with an exact definition of a neural or physiological phenomenon that we intend to investigate.…”

Bringing Back the Person into Behavioural Personality Science Using Big Data

“…This reliability depends on high effect and relative stability of data. Grandy, Lindenberger and Werkle‐Bergner (2017) suggest increasing data density by using repeated measurements as a possibility to enhance reliability. However, the reliability gain is not necessarily proportional to the density increase.…”

“…Although Windelband (1904) did not restrict the idiographic approach to the study of individual persons, the call for a careful analysis of the individual person as an alternative to the analysis of aggregates was echoed throughout the history of personality psychology (Allport, 1937; Beck, 1953; Beck & Jackson, 2020a; Carlson, 1971; Lamiell, 1981; Magnusson, 2001; Shoda, Mischel, & Wright, 1994; Stern, 1911), and there are indeed idiographic studies in personality science that are but low in number compared with the vast amount of nomothetic research (e.g. Allport, 1965; Beck & Jackson, 2020a; Cervone, Mercurio, & Lilley, 2020; Grice, 2004; Hermans, 1988; Karch, Sander, von Oertzen, Brandmaier, & Werkle–Bergner, 2015; Nasby & Read, 1997; Pelham, 1993; Schmitz & Skinner, 1993; Shoda et al, 1994; Simonton, 1998).…”

“…At the same time, attempts to reconcile the idiographic/nomothetic divide had been proposed from the very beginning (Allport, 1961; Bem, 1983; Falk, 1956; Grice, 2004; Hermans, 1988; Krauss, 2008; Lamiell, 1981; Magnusson, 2012) and recently also with regard to statistical procedures (GIMME = group iterative multiple model estimation; Gates & Molenaar, 2012; Beltz, Wright, Sprague, & Molenaar, 2016; Wright et al, 2019). The possibility to reconcile and integrate idiographic and nomothetic approaches in personality science is also implied in the last two of three different meanings of the term idiographic Krauss (2008) identified based on a review of self–declared idiographic research in the literature: the first meaning of the term idiographic relates to approaches that aim at describing the uniqueness of a single person while denying general laws.…”