What is a Cohort Study?

1. Sub-brand to go here What is a Cohort Study? Jane Elliott Director of the Centre for Longitudinal Studies July 2012 CLS is an ESRC Resource Centre based at the Institute of Education

2. Objectives • Introduction to the content and design of the British Birth Cohort studies at CLS • Further examples of cohort studies • The distinction between a cohort study and a panel study • Examples of recent research using cohort data • Examples of how cohort studies have had an impact on policy • How to find out more/access the data

3. British Birth Cohort Studies • 1946: MRC National Survey of Health & Development • 1958: National Child Development Study • 1970: 1970 British Birth Cohort Study • MCS: Millennium Cohort Study — first national birth cohort study for 30 years (2000-1) • Plans for a 2012/2013 cohort study

4. A Roman Cohort? A cohort ....individuals moving or progressing as a unit

5. 1958 Birth Cohort Study • Sample of over 17,000 infants born in 1958 (perinatal mortality study) • Sample followed at ages 7, 11, 16, 23, 33, 42, 46, 50 (biomedical at age 44) • Multipurpose study: family life; education; employment; skills; housing; health; finances; citizenship • Approximately 10,000 individuals are still participating • Mainly quantitative – highly structured interviews, but qualitative interviews with a subsample of cohort members at age 50 • Core funded by ESRC with data collected every four years (five years after age 50)

7. Exam results Aspirations Voting behaviour Training and skills Savings Gets married Born 1958 1st Child 1984 2nd Child 1987 Age 11 x Age 7 Job 1 Job 2 Job 3 Psychological well being Domestic division of labour Working hours preferences Union membership Hypothetical life history Parents’ social class Parental divorce Age 16 2000 2004 1991 1981 Age 23 Age 42 Age 46 Age 33 Mother smoking Parental interest in school work Free school meals Maths and reading tests Teachers’ assessment of child’s behaviour

8. Structured interview at age 50 • Household composition, marital status etc • Housing • Relationships & domestic division of labour • Children and parents • Family income • Employment and Partner’s employment • Pensions & attitudes to retirement • Qualifications, training and skills • Health (including menopause) • Alcohol consumption and smoking behaviour • Memory & Concentration • Voting behaviour, social participation & social support • Well-being • Consent to record linkage

9. Overview of the 1970 cohort study • BCS70 is a multi-disciplinary longitudinal study following the lives of over 17,000 individuals born in Great Britain in one week in 1970 • There have so far been 8 sweeps of data collection: (Birth, 5, 10, 16, 26, 30, 34 and 38) • The 9th sweep will take place in 2012 when study members will be aged 42: • 75 minute face to face interview • Additional self-completion questionnaire (paper or online) • Funded by ESRC

10. Overview of the Millennium Cohort Study Oversamples for Scotland, Wales and Northern Ireland, areas with high child poverty and, in England, areas with higher ethnic minority populations Over 19,000 children born in the UK between September 2000 and January 2002 Follows children throughout their lives Fifth survey, when children are in their last year of primary school Funded by ESRC and UK government departments One of five British Birth Cohort Studies

11. What have we done before? And what’s new?

12. Narrative elements of cohort studies • Allow us to trace lives through time & understand how childhood circumstances may impact on adult outcomes • Potentially allow for the construction of individual case studies based on detailed information collected over the years (while preserving confidentiality) • Allow for a focus on the historical context which has helped shape individual experiences • Comparisons between cohorts can enable the development of a narrative about social change

13. 50 46 42 38 34 33 30 26 23 16 16 11 10 7 5 Cohort Comparisons Life cycle effects

14. Source: Exploring Data (C. Marsh 1988) Figure 6.1 Unemployment as a problem in Britain: actual and perceived Source: unemployed claimant count: Employment Gazette Decembet 1982 and May 1986. Percentage naming unemployment as most or second most urgent problem facing the country: Gallup Political Index monthly.

15. Proportion of women in paid employment, by age and cohort Source: Jenny Neuburger - Paper presented at CLS June 2008

16. What is the difference between a cohort study and a (household) panel study? Cohort Study Panel Study Sample of adults representative of whole age range Questions need to be applicable to all Sample spanning different ages allows for description of whole population Focus on household dynamics and transfers Data collection every year or perhaps every two years Perhaps less likely to have a focus on health/bio-medical data • All individuals in the sample are the same age • Data collection focussed on specific life stage • Large sample of the same age facilitates modelling of specific life transitions • Focus on individual trajectories (limited info about other hhold members) • Data collection may be less frequent (e.g. British Birth Cohort Studies) • Objective health measures in childhood – resource for biomedical research

17. Children’s Essays Biographical Interviews at age 50 Open ended question at age 50... ‘Imagine you are 60’ Qualitative Resources

19. Social participation project: Qualitative Sub-study of NCDS 2008 • ESRC funded a qualitative component of the 2008 sweep of the 1958 cohort study • Initial aim to interview 180 cohort members in 3 separate areas of Britain • 170 interviews carried out in England and Scotland and a further 50 in Wales • Aim to provide archived qualitative data for secondary analysis, together with the existing quantitative datasets • Joint project with CRESC at Manchester: Jane Elliott; Andy Miles; Sam Parsons; Mike Savage • Funded by the ESRC Research Resources Board

20. Structure of the interview and topic guide • Interview in six sections: • Neighbourhood and belonging • Social participation and leisure activities • Friendships • Life story and trajectories • Identities • Experience of the NCDS • Visual exercises also included – personal community maps and life trajectories • Aim for an average of ninety minute interviews • Interviews digitally recorded and transcribed verbatim • Interviewers also wrote a brief summary of the interview • Interviews to be anonymised and deposited at the UK data archive

21. Age 50 self-completion questionnaire • At age 50, in 2008 NCDS Cohort members completed a 16-page paper self-completion questionnaire, including questions about health and well being and a personality inventory. • The final question stated: • Imagine that you are now 60 years old...please write a few lines about the life you are leading (your interests, your home life, your health and well-being and any work you may be doing). • Mean length of 7383 responses: 57 words • All of the 7383 responses have been transcribed and are being documented and prepared for deposit at the data archive.

22. Basic Skills – a major policy concern in Britain

23. The value of basic skills in the British labour market: Vignoles, De Coulon and Marcenaro-Guierrez (Oxford Economic papers 2011) • Aim to evaluate the labour market value of literacy and numeracy • Draw on literacy and numeracy tests carried out with the BCS70 cohort at age 34 in 2004. • Make use of test score information collected during childhood and also information on qualifications and employment history in order to isolate the impact of basic skills on wages • Cross cohort analysis carried out to assess whether the wage return to skills has changed over time. • Richness of data from the cohort studies allows proper control for a wide range of observable characteristics.

28. The value of basic skills? Vignoles, De Coulon and Marcenaro-Guierrez (Oxford Economic papers 2011) • Models demonstrated that literacy and numeracy skills have a significant relationship with earnings even for individuals with similar levels of education • The effects appear to be very similar for both men and women • One standard deviation difference in skill levels is associated with approx 15% increase in earnings • Cross-cohort comparisons suggest that the value of basic skills has remained stable over time – this implies that the increase in supply of skills has been matched by an increase in demand for skilled workers

29. Poverty, family resources and children's early educational attainment: the mediating role of parenting (Kiernan and Mensah, 2011, British Ed Research Journal) • Uses longitudinal data from first three waves of MCS (N=5462) • Focus on both episodic and persistent poverty • Outcome measure is based on the Foundation Stage Profile collected from teachers when children were aged 4-5 in the first year of primary school • Equivalised family income was used to measure poverty • Family resources index was also constructed: income poverty, mother’s education, family employment, housing tenure, quality of the local area, mother’s age at birth of her first child, family structure, number of children in the household, child’s birth order, child’s ethnic origin and the language spoken in the home • Parenting measure constructed using reports of activities with child and interviewer observation

30. Poverty, family resources and children's early educational attainment (results summary) • Children from poor families and those with low levels of family resources are doing worse in their first year of school • Poverty matters but persistent poverty is even more detrimental • The parenting index was also a very important factor predicting children’s early educational attainment • Positive parenting matters regardless of the levels of resources in the family • A decompositional analysis suggested that about one-half of the effects of child poverty and 40% of resource disadvantage may be accounted for by the quality of parenting the child has received in early childhood

31. How do I access the data? • Data is available via the Economic and Social Data Service based at the University of Essex • Data is free for non-commercial use (e.g. teaching and research) • Following a simple registration procedure data can be downloaded directly from the Economic and Social Data Service website • Information about what questions have been asked is provided via the CLS website but we can also answer individual enquiries about specific topics. • Plans to make more potentially disclosive data available via the Secure Data Service at the University of Essex: • http://securedata.data-archive.ac.uk/home

32. CLS Birth Cohort Studies: Web Resources • Resources available via CLS website: • (www.cls.ioe.ac.uk/Cohort/mainncds.htm) • Searchable bibliography (over 2000 articles, chapters etc) • Briefings (summaries of recent findings) • Annotated Questionnaires and CAPI Documentation • Technical Reports – e.g. on sampling, instrument development and fieldwork of MCS • Data Dictionaries • Events and workshops

33. Policy relevance of 1958 and 1970 cohort studies • The health impact of smoking in pregnancy • Child poverty • Declining intergenerational mobility • Antecedents and consequences of disability • Health continuities over the lifecourse and health inequalities • Determinants of crime and anti-social behaviour • Social and economic returns to education and training • Access and barriers to higher education • Improving adult basic skills • Women’s opportunities in employment • Maternal employment and child outcomes

34. Conclusions: research questions best addressed by birth cohort data • Long term outcomes of experiences and decisions in early life • Medium and short-term outcomes & links between different life domains (e.g. health and employment) • Descriptions of individual trajectories – careers, relationships, fertility, poverty and disadvantage • The links between social change and the changing experiences of different cohorts • Intergenerational transmission of advantage and disadvantage and the processes involved

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36. Overview of the Cohort Resources Facility

37. Leadership team WP5: Data linkage administrative data WP7: Data linkage – health data WP1: Harmonisation of biological structure and function WP2: Harmonisation socio-economic resources WP3: Harmonisation analysis of biological samples WP4: Harmonisation measures of vision WP6: Data linkage - geography 1946 cohort 1958 cohort Cohorts’ College Cohorts’ repository 1970 cohort ALSPAC Impact MCS Understanding Society Metadata SWS Training and capacity building HCS New BCS Uniform Search Platform

38. Achieved sample size in previous sweeps BCS70 Sample size (Previous sweeps) - additional information Age 38 Telephone Survey Response

39. A different cohort design – the Hertfordshire Cohort Study

40. Live births in Hertfordshire recorded in Health Visitor’s ledgers 39,764 Hertfordshire Cohort Study: structure 1931-1939 1998-2003 1998-2003 2005 2008 Traced and living in Hertfordshire 8,650 Home interviews 3,225 Clinic visits 2,997 Musculo-skeletal follow-up 642 Clinical outcome questionnaire 2,225 Dead 215

41. Hertfordshire Cohort Study: measurements • Historical records: Birth weight, weight at one year • Infant feeding/infections • Questionnaire: General health • HRQoL: SF36 • Diet: FFQ and 24 hr diary • Physical activity • Clinic visit: CVD: blood pressure, ECG COPD: spirometry • Type 2 DM: anthropometry, OGTT • Osteoporosis: DXA • OA: Hand & knee x-ray • Sarcopenia:strength, anthropometry, pQCT • Frailty: Fried score, Rockwood index • Wellbeing: WEMWB Scale • Venous blood: Glucose, insulin, bone turnover, DNA Syddall et al Int J Epidemiol 2005

42. Hertfordshire Cohort Study: geography Baldock Royston Welwyn Garden City Hertford Radlett Southampton

43. Hertfordshire Cohort Study: history