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Working and ageing
92 Guidance and counselling for mature learners

5.2. Methodological considerations

There are several methodological considerations when discussing cognitive
ageing. As mentioned above pathological and non-pathological ageing form
a continuum, so it is inevitable that some studies will include participants with
a pathological condition in their sample. Another issue is isolating the age
factor when interpreting results. Cognitive ageing is a multifaceted
phenomenon affected by various factors which makes it difficult to find cause
and effect relationships even in the most controlled studies. Most empirical
evidence is based on cross-sectional studies that typically compare younger
with older adults simultaneously. The observed differences in performance
are explained in relation to the age factor but there are other possible
explanations; for example premorbid intelligence is considered a significant
predictor of cognitive performance in older adults. In addition, there may be
other confounding variables, such as lifelong training and lifestyle that may
improve or underpin differences between the two populations (Hedden and
Gabrieli, 2004). Ideally, longitudinal studies, which involve following-up the
same participants across the life span, would provide more coherent
information on cognitive ageing. Such studies are more difficult to perform as
they require long-term data collection and need a large cohort that will
inevitably decrease over the years.
Deary et al. (2009) noted that although the profile of normal ageing is well
established, with some cognitive abilities being more affected than others, the
factors that underpin cognitive decline are weakly supported by empirical data.
Most studies show small effect sizes (<0.20 according to Cohenʼs
conventions). Cohen (1988) conceptualised effect sizes as a measure of the
strength of the relationship between two variables. Having small effect sizes
essentially means that the effect of each factor on cognitive ageing is small
but can be statistically significant. Some studies show methodological
inaccuracies that are difficult to replicate and other studies find contradictory
results. Despite these methodological considerations, research has provided
substantial information on non-pathological cognitive ageing and has provided
significant information of the factors that determine successful ageing.