In this study, based on a longitudinal national population-based sample, the primary aim was to examine whether there were continuing effects of education over the life course on cognitive ability in midlife with specific attention to the relationship between adult education by 43 years and cognitive ability at 53 years. The secondary aim was to characterize selection into adult education, defined largely in terms of occupational training, but also including attendance at evening courses. Regarding the first aim, independent of cognitive ability, we found that educational attainment completed by early adulthood had a strong association with higher verbal ability and verbal memory in late midlife at almost all qualification levels and with verbal fluency (animal naming) and mental speed and concentration (timed letter search) at the two highest qualification levels. The continued effects of education were apparent in the associations between adult education at all levels and higher verbal ability and verbal memory, as well as verbal fluency at the level of participation without qualifications in late midlife. We found no association between adult education and mental speed and concentration. The adult education and midlife cognitive ability associations were independent of prior cognitive ability, formal educational attainment, and adult social class attainment and mobility. In terms of the second aim, we showed that men from nonmanual occupational social class of origin and in adulthood and having greater formal educational attainment by 26 years had an increased likelihood of participating in adult education.
The continued effects of education through participation in adult education, a small but valuable intervention, appeared to confer a modest benefit to verbal ability, memory, and fluency in the fully adjusted models, as expected. Our principal hypothesis, that adult education would be independently associated with higher verbal-based measures of cognitive ability in midlife was, therefore, confirmed through significant associations with verbal ability and verbal memory, although only partially confirmed through its relationship to verbal fluency in the fully adjusted models. Our findings supported our secondary hypothesis by showing that adult education was not related to speed and concentration, representing time and visual search tasks, consistent with the weak association between formal education and this measure (
Richards & Sacker, 2003). Our findings were also consistent with those of the Seattle Longitudinal Aging Study, which showed verbal memory to improve over the adult life course, peaking at around age 60 years (
Schaie, 1996). In contrast, perceptual speed, which in part underlies the letter search task, showed a systematic decline from a peak in early adulthood.
Controlling for prior cognitive ability at two time points reduced the likelihood of reverse causality. Additionally, we adjusted for mobility between manual and nonmanual social class from ages 26 to 53 years to decrease the possibility that adult education leading to occupational advancement was a confounding factor. We should note, however, that regressing adult cognitive ability on educational attainment and another measure of cognitive ability is noninformative if the correlation between these variables is due to a common cause, such as genetic potential (
Dickens & Flynn, 2001). Nevertheless, we argue that our results represent an association between adult education and midlife cognitive ability.
It is interesting to note that adult education without qualifications was associated with higher verbal ability and fluency scores than was adult education leading to a qualification. Given that adult education was more likely to have been undertaken by those with formal qualifications by 26 years, it may be that further qualifications achieved through adult education bestow no extra benefit to verbal fluency beyond that conferred during the school years. For verbal ability, obtaining qualifications through adult education courses confers less benefit than undertaking adult education without qualifications. In contrast, the greatest benefit for verbal memory at 53 years came from completing adult education with qualifications beyond the O level.
In addition to these main findings, the pattern of associations between social mobility and verbal memory is worthy of comment. As expected, those in manual occupational social class at ages 26 and 53 years, and those in nonmanual social class at both these ages, had, respectively, the lowest and highest mean NART scores in the sample. In the fully adjusted model, upward mobility (manual to nonmanual) was associated with an increase in verbal memory score of almost equal magnitude to that of those consistently in nonmanual class. As would be expected, being upwardly mobile resulted in higher verbal ability scores than being stably manual and relatively better scores than being downwardly mobile, but less than being stably nonmanual social class. We did not observe these associations for verbal fluency and speed and concentration.
These findings, along with the independent association of adult education and midlife cognitive ability, corroborate evidence that cognitive ability is capable of modification over the adult life course. Other longitudinal studies have also shown fluctuations in cognitive test performance, in adulthood (
Arbuckle et al., 1998;
Rabbitt, 1993;
Schaie, 1996) as well as in childhood (
Caspi, Harkness, Moffitt, & Silva, 1996;
Feinstein & Bynner, 2004). Corroborating evidence for such modifiability of cognitive ability comes from a range of sources. The “Flynn effect” (
Flynn, 1987,
1999) refers to secular IQ rises in Western countries that cannot be accounted for by changes in the gene pool, although these may be partly based on improvements in nontransferable skills through increased familiarity with test materials and conventions (
Neisser, 1998). However, there are within-family variations in IQ, such as its inverse association with birth order (
Zajonc & Bargh, 1980), as well as environmental influences on IQ beyond the family, such as the effect of neighborhood (
Blau, 1981). This evidence was supported by adoption studies that demonstrated substantial gains in IQ in high-risk children removed to more advantaged homes (
Duyme, Dumaret, & Tomkiewicz, 1999;
Rutter, 1998;
Schiff & Lewontin, 1986). Finally, cognitive function can be changed through early learning and school readiness interventions (
Caspi et al., 1996;
Ramey & Ramey, 2004).
We should note two possible limitations of the present study. First, there are important distinctions to make in assessing the benefits of adult learning that extend beyond the broad and inclusive measure of adult education available in these data. Adult learning experiences vary in terms of the availability of accreditation, the level of accreditation, the curriculum (e.g., academic or vocational), the mode of learning (e.g., classroom or distance learning), the location (e.g., community center, workplace), and duration (e.g., occasional evening study for one term, full-time higher education degree over several years;
Feinstein & Hammond, 2004;
Vignoles et al., 2003). Nonetheless, it is important to note that these data allow for the differentiation between adult education participants and nonparticipants, as well as between accredited and unaccredited courses. The measure is broader than we would have preferred; however, few longitudinal, large-sample data sets include these types of detailed measures, and even fewer also contain measures of prior and subsequent cognitive development over the life course. Although more detailed measurement would help to differentiate the which aspects of adult education may have an impact cognitive ability, our primary aim of discovering whether there was an independent association between participation in adult education on midlife cognitive ability, independent of prior cognitive ability, was possible with our inclusive adult education measure. Second, our results may have been influenced by selection bias. Adults with higher prior cognitive ability may be on life paths of greater cognitive skill development (i.e., less decline in functioning and/or more cognitively challenging activities) and more likely to engage in adult learning. Although we have no reason to conclude that the selection bias was substantial in this study (i.e., we found benefits of adult education at all levels of formal education by 26 years and at every level of the cognitive ability trajectory from 8 to 26 years), the statistical associations may represent, in part, this underlying factor rather than an association that was solely due to the benefits of adult education.
With these limitations in mind, how should one interpret the association between adult education and midlife cognitive function? Verbal ability, as indexed in this study by the NART, is sometimes referred to as
crystallized intelligence, a term originally coined by
Horn and Cattell (1966) and defined by
Carroll (1993, p. 599) as “a type of broad mental ability that develops through the ‘investment’ of general intelligence into learning through education and experience.” Although this definition implies that those of high general intelligence are likely to seek (invest in) education and other enriching experiences, our findings strongly suggest that the reverse causal pathway (i.e., that these experiences also augment cognitive ability) is equally likely. This applies (a) to verbal ability as measured by the NART, which by design depends on the acquisition of information, and also (b) to memory, with possible implications for the reduction of dementia risk in old age (
Gauthier et al., 2006). The positive influence of adult education on verbal ability may also reflect improvement in literacy, with important consequences for skilled daily function, employment retention, and career progression (
Bynner, 2004).
The association between adult education and cognitive ability also has important public health implications. Unlike in formal schooling, which is compulsory to age 16 years in the United States and United Kingdom, individuals potentially have more agency in choosing to take up adult education, whether driven by economic need, by career considerations, or by a love of learning. The structure of the U.K. educational system below the higher education level may allow for more opportunities to obtain a variety of accepted qualifications at any age. For example, instead of a single high school diploma or qualification for completion of minimum schooling, U.K. students take examinations for the General Certificate in Secondary Education or O levels. Each subject has a separate exam, with students taking exams in as many as 12 subjects. Individuals seeking entrance into higher education will then go on to take advanced-level exams (
Department for Education and Skills, 2007). However, despite the U.K. system including more opportunity for concentration in specific subjects, there is no evidence to suggest the benefits of adult education are less in the United States.
Therefore, the characteristics that increase the likelihood of participation in adult education, or at least reduce the barriers to access, are particularly important to note. Our results indicated that participation was more likely for those with formal educational qualifications and higher social class positions, results that are broadly consistent with those of
Gorard and colleagues (2001). Ideally, policies and programs should be directed toward increasing adult education in midlife and later life among those educationally and economically disadvantaged, and they should emphasize personal development goals in addition to accredited learning (
Aldridge & Tuckett, 2005).
The benefits of adult education for cognitive ability in late midlife, although modest, have implications beyond increasing a skilled labor market and may help to delay cognitive decline, with potentially important benefits for independence, social integration, and well-being in later life (
Panza et al., 2005). Verbal ability, a proxy for cognitive “reserve” (Richards & Deary, 2004), may protect against the clinical expression of disease (e.g., from neurodegenerative processes underlying Alzheimer's disease). Unlike other measures of cognitive functions, it is relatively resistant to age- or morbidity-associated decline. In contrast, impairment in learning and memory (word-list task) is arguably the most pathonemonic of all neuropsychological findings for Alzheimer's disease, a disorder that is associated with severe loss of independence and quality of life, whereas verbal fluency (animal naming) and visual perception and cognitive speediness (timed letter search) reflect different aspects of skilled daily functioning. The positive association between education and a wider range of health and functioning is well known (
Mirowsky & Ross, 2003). It will, therefore, be important for further research to examine whether similar health benefits are gained or continued through adult education.
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