What’s It All about: Variation and Aging

Those of us who arrived at the study of cognitive ageing following a traditional experimental approach have long searched for ways to understand the ‘noise’ in our data. This noise was a ‘nuisance’ that often arose from cross-sectional studies. Through them we crudely sought to understand ageing as a process, while relying on data derived from studies where age and cohort were inherently confounded and single observations were made at one point in time. To the extent that human development is all about intraindividual change, this approach was flawed, but reflected at least two beguiling assumptions. One was that the confounding of age and cohort might not be so crucial in the study of such basic processes as cognition. Although Schaie and others [1] have shown repeatedly that this is not the case, still the experimentalist forged on. We also held to a belief that observation of age by condition interactions would show the way to what ageing was all about. What we didn’t realize at the outset was that these interactions are exceptionally elusive. The ‘hum’ in the system partially contributed to this, but the way forward was not obvious. One thing that is clear in the series of papers that follows is that there is both a need, and many ways, to harness interindividual differences, intraindividual change and interindividual differences in intraindividual change to enable us to better understand ageing. The return of a more psychometric approach to understanding ageing has been in no small part a contributor to this methodological shift. The content area of these papers derives mainly from cognitive and sensory ageing, but the lessons to be learned here are readily transferable to other domains. Is this emphasis because these constitute two of the areas most relevant to day-to-day functioning and quality of life? Perhaps it derives from our having developed exquisitely sensitive barometers to index cognition and the impact of sensory processes. Regardless, the challenge will be to (a) establish efficient as well as efficacious ways to undertake research that will not overtax our participants or our research resources and (b) extend these approaches to social and affective domains. As a whole this series of papers raises important questions about how we conceptualize the ageing process. While the emphasis is on the statistical end of a theorymethod continuum, the inseparability of these elements of analysis becomes obvious in each paper. The contributors develop theoretically-driven hypotheses about what could happen, given specific patterns of overall statistical relationships. The core group of authors of these papers are part of a new generation of researchers of cognitive ageing who want to push the boundaries of evolving statistical techniques to re-visit old questions, e.g., of neural noise, fluid and crystallized intelligence and how gains at one point in time benefit later performance. They also emulate the