Assessment and harmonisation of cognitive measures in five British birth cohorts

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In a project funded by CLOSER and led by Dr Vanessa Moulton (Centre for Longitudinal Studies, UCL), with support from Dr Eoin McElroy (Lecturer in Psychology, University of Leicester), 180 cognitive measures administered to participants and their families in five British Birth cohorts have been consistently documented for researchers to use.

What is cognition?

Cognition is a broad term that refers to individual differences in mental capability. It encompasses many different mental processes such as perception, learning, memory, and reasoning. As it can impact on many different aspects of life, cognition is widely researched across many fields. However, its conceptualization, and the terms used to describe it, vary across these different scientific disciplines. For instance, the term ‘cognitive ability’ is most often used in psychology and education, economists mostly refer to ‘cognitive skills’, whereas ‘cognitive functioning’ is usually preferred in medical disciplines.

Measuring cognition in the British cohorts

The CLOSER British birth cohorts contain a wealth of information on cognition over the life course and across different generations. Indeed, the cohorts have been tracking the cognitive ability of the population for decades, with the earliest tests often devised specifically by educational experts for the cohort study in question. In the more recent cohorts, standardised ability tests, such as the British Ability Scales (BAS) and Wechsler Intelligence Scale for Children (WISC) have been employed. As well as the cohort members completing cognitive tests, in some cohorts, tests have also been administered to their parents, as well as to the cohort members’ children. In all, 180 cognitive tests have been administered to participants across the five British birth cohorts. These tests have been used to answer research questions in many different fields, ranging from psychiatry and psychology to economics and education.

Many of these tests, however, differ considerably from one another both within and across the studies. For instance, the cognitive tests used in childhood often measure aptitudes that are reflective of scholastic achievement (e.g. reading, writing, arithmetic), whereas tests given to adults are more likely to capture skills that are important for everyday life (e.g. memory, processing speed). Over time, the younger birth cohorts have moved away from traditional pen and paper assessments to computer assisted tests. These differences can make it challenging when comparing trends across the life course or findings across cohorts.

Introducing our online guide of cognitive measures for researchers

Given the sheer number of tests administered, using these tests can be a daunting and time-consuming process for researchers, and there is considerable heterogeneity in the quality and quantity of the documentation used to describe these cognitive assessments. To date, there has been no attempt to develop a uniform description of the key features of these instruments.

Thanks to funding and collaborative support from CLOSER, we have been able to develop an online tool (also available in hard copy) in which we provide a comprehensive description of the cognitive measures that are available in five British birth cohorts:

  1. the MRC National Survey of Health and development (NSHD);
  2. the 1958 National Child Development Study (NCDS);
  3. the 1970 British Cohort Study (BCS70);
  4. the Avon Longitudinal Study of Parents and Children (ALSPAC); and
  5. the Millennium Cohort Study (MCS).

This easily searchable guide to the measures is available on the CLOSER website. It provides key information on the cognitive tests in a consistent format. We detail when, how and where tests were administered, what cognitive skills/abilities were measured, how the tests were scored, and what variables correspond to the tests, as well as basic descriptive statistics. We also provide key references for each measure, the original source of the test, details of useful technical resources and a link to the original questionnaire. With overview tables of the tests, cognitive measures can easily be explored by life stage or by cohort.

A valuable resource for researchers at all stages of their careers

The consistent documentation of the cognitive measures is a useful resource for researchers at all career stages. Not only do we provide a detailed outline of the measures available, we also highlight when and where the same or conceptually similar tests have been administered. We have done this by classifying each test by the specific ability it is reported to measure according to the Cattell-Horn-Carroll (CHC) model of cognitive ability. The CHC model, multi-dimensional and hierarchical in nature, ranges from general ability (g) to broad, narrow, and specific abilities – a glossary of the abilities are outlined in the report. Classifying each test under a consistent theoretical framework will allow researchers to include theoretically consistent measures of cognition in their studies, which is an important first step in facilitating developmental and cross-cohort research.

Looking forward

High quality longitudinal data is required to improve our understanding of the development and decline of cognitive ability. The British birth cohorts used represent a key data resource in this regard. Our online guide can help facilitate future research and inform the development of assessment waves and the next generation of cohort studies, by helping to maximise the comparability of measures. Only by pooling comparable data from different cohorts can we fully understand how cognition develops across the life course, and the factors that both promote and impede its development.

In addition to the launch of the online cognitive measures guide, we have an upcoming report on how to maximise the comparability of these measures within and across cohorts (i.e. retrospective harmonisation). This information will be useful for researchers who are interested in developmental and cross-cohort (inter-generational) trends in cognition. Sign up to CLOSER’s longitudinal newsletters to stay in the know.

Explore the online cognitive measures guide

Further information: