Resistividad y efecto Hall Técnica de van der Pauw

This section describes the research design and methodology used in the ALSPAC study.

3.6.1 ALSPAC research design

3.6.1.2 Selection of a birth cohort study

Longitudinal research requires data at two or more time points, with the same individuals analysed from one period to the next (Menard 2007). There are primarily two types of longitudinal designs, cohort studies and panel studies. A cohort study is that which is formed from a sample on the basis of a shared characteristic, e.g. birth year, whilst a panel study is that which in which the sample do not always have a shared characteristic (Mason and Wolfinger 2001). Panel surveys are distinct from cohort studies, as they typically sample from the entire age range and collect repeated measures throughout the life course, whilst cohort surveys often sample an age cohort born in a particular year and follow that cohort at infrequent intervals, often with a focus on early childhood development (Menard 2007). To enable a sequence of events to be established in early

65 childhood, whilst also enabling change at the individual level to be

assessed, birth cohorts were the favoured approach. This enabled the examination of how multiple risk factors of PCRQ and school

connectedness ‘interacted in concert’ in early years to predict the

development of alcohol, tobacco and cannabis use at 17 years (Glaser et al. 2010).

3.6.2.2 Consideration of potential data sources

There are many high-quality UK cohort studies which contained data on adolescent use of alcohol, tobacco and cannabis. These included the Millennium Cohort Study (MCS), the British Household Panel Survey (BHPS; British Young Peoples Survey/Understanding Society), the Cambridge Study in Delinquent Development (CSSD), the Edinburgh Study of Youth

Transitions and Crime (ESYTC), the Belfast Youth Development Study (BYDS), the Longitudinal Study of Young People in England (LSYPE) and the Avon Longitudinal Study of Parents and Children (ALSPAC). To select the most appropriate data source for this study, a screening criterion was developed (see Appendix 4). The criteria were having assessments of alcohol, tobacco and cannabis use in late adolescence, alongside prior measures of PCRQ and school connectedness. Each cohort study is described as follows.

The Millennium Cohort Study (MCS) is a longitudinal birth cohort study following approximately 19,000 children born in 2000/01 in the UK

(England, Wales, Scotland and Northern Ireland). It is one of the UK’s most recent birth cohort studies, tracking Millennium children from early

childhood to present day. The study is advantageous in that it includes participants from all of the UK and collects data for: parenting; childcare; school choice; child behavior and cognitive development; child and

66 housing, neighborhood and residential mobility; and social capital and ethnicity (UCL 2018). However, at present, the MCS only has six waves of participant data: 9 months; 3 years; 5 years; 7 years; 11 years; and 14 years (UCL 2018). Due to this study examining use of alcohol, tobacco and

cannabis in late adolescence and the MCS not collecting data for those aged 17 years until 2018 (UCL 2018), this was not a suitable source of data for the study.

The British Household Panel Survey (BHPS: British Young Peoples Survey/Understanding Society) is an annual household panel survey of approximately 5,500 nationally representative households, recruited in 1991. It is advantageous in that contains approximately 10,000 participants who are re-interviewed each successive year and still followed if they split from the original household. Similarly, new members joining households in the sample become eligible, with children interviewed when reaching 16 years of age. Since 1994, children aged 11-15 also complete a short interview. In 2009, the BHPS sample was merged with Understanding Society (the UK household Longitudinal Study (UKHLS)). Understanding Society currently contains eight waves of completed data (USOC 2018) and is unique in that it contains an ethnic minority boost (Berthoud et al. 2009). It contains measures on alcohol, tobacco and cannabis use under 18 years of age, alongside parental and school measures in earlier years. However, the school measures are limited in that they do not specifically measure school connectedness, instead focusing upon truancy, homework, parental involvement in education, misbehaviour in school and bullying (USOC 2018b). Therefore, not suitable for this study.

The Cambridge Study in Delinquent Development (CSDD) and the Edinburgh Study of Youth Transitions and Crime (ESYTC) were also dismissed as potential data sources. Although containing childhood

67 measures, the Cambridge study was dismissed as measures were not available to effectively assess PCRQ and school connectedness. Further, the sample was drawn in 1961 from an inner area of London and comprised of only males (Muncie 2004) which presents problems in terms of

generalisability and bias. Although ESTYC is a more recent study, being established in 1998, it was also dismissed for not containing measures of PCRQ and school connectedness, alongside the study only following participants initially over a 5 year period (Aston 2015; ESTYC 2018).

Limited measures of PCRQ and school connectedness were also seen in the Belfast Youth Development Study (BYDS) and Next Steps, the more recent version of the Longitudinal Study of Young People in England (LSYPE). Even though the BYDS is unique in that it is a UK study of adolescent drug use, the study did not start until 2001 and comprised of yearly data collection from approximately 4,000 young people between the ages of 11-12 years of age. As children were aged 11-12 at baseline, no earlier measures of parent child relationships were available. As this is important feature of this study, the BYDS was not a potential data source. Next Steps is also a large study started in 2004 with the yearly data collection from about 16,000 children living in England (UCL 2018b). However, no childhood measures of parent child relationships or school connectedness were available.

The Avon Study of Parents and Children (ALSPAC) was given consideration as it is one of the largest ongoing UK population-based birth cohort studies, established to understand how both genetic and environmental

characteristics can influence health and development in children (Fraser et al. 2012). ALSPAC initially enrolled a cohort of 14,541 pregnancies, with 13,973 eligible participants at 1 year. ALSPAC is advantageous in that its scale and richness is unprecedented in epidemiological studies (Fraser et al.

68 2012), currently containing a total of 33 child completed questionnaires across ages of 65 months to 23 years. Area’s covered within the

questionnaires, at multiple time points, include parenting, school

connectedness and use and hazardous use or a screener for dependency on alcohol, tobacco and cannabis. It collects in depth data on PCRQ and school connectedness in childhood, alongside detailed data on adolescent alcohol, tobacco and cannabis use in addition to dependency. It was selected as the data source for this study.

3.6.2 ALSPAC study methodology 3.6.2.1 History of ALSPAC

ALSPAC contains a core-sample of 14,541 pregnant women who were expected to deliver their infants between April 1 1991 and December 31 1992 from Avon, UK. All were invited to participate in the study, which was set up to collect comprehensive socioeconomic and health related data on a large population sample of new-born children and their parents

throughout early pregnancy and childhood. A total of 13,973 singletons and twins who were alive at 1 year and their mothers were eligible for the study, with children now 23 years of age. Since 1991/92 the children’s development and health has been followed by collecting genetic and environmental information through questionnaires, clinics and lab-based assessments. At 17 years, a total of 105 postal questionnaires had been administered (19 carer-based, 23 child-based answered by the carer, 24 child-completed, 16 partner-based, nine puberty and 14 school-based). Additionally, since age 7 years, ALSPAC children were annually invited to nine walk-in clinics comprising of computer tasks, individual interviews and focus group interviews (Fraser et al. 2012).

69

3.6.2.2 ALSPAC attrition

Despite efforts to maintain levels of participation, the number of ALSPAC participants has reduced over time, from 13,973 at baseline to 3,372 at child age 18 years 7 months. Attrition rates throughout the study were greatest when children participants were less than 33 months old and again when they were over 13 years of age (Boyd et al. 2013). Over 9,467 participants have completed at least 10 questionnaires (Fraser et al. 2012). However, at 13 years of age, only 48.2% of 12776 eligible participants had complete data for all 12 waves (Boyd et al. 2013).

3.6.2.3 ALSPAC representativeness

ALSPAC representativeness has been described retrospectively at various time points, using several information sources. In 1991, at child age of under 1 year, comparisons were made between ALSPAC mothers, mother’s resident in the Avon area also with a child under 1 year and 1991 UK census data (ALSPAC 2018). Table 4 shows that ALSPAC mothers were more likely than both Avon and UK mothers to live in owner occupied accommodation, have a car, be married and be of white ethnicity. This is similar to all studies where a representative sample has been attempted (ALSPAC 2018).

Table 4: Comparison of UK, Avon and ALSPAC mothers with children less than 1 year old in 1991

Socio-economic characteristic UK Avon ALSPAC Owner occupier 63.4% 68.7% 79.1% 1+ person/room 30.8% 26.0% 33.5% Car in household 75.6% 83.7% 90.8% Married couple 71.8% 71.7% 79.4% Non-white mother 7.6% 4.1% 2.2%

70 At child age of 16 years, the sample contained an overrepresentation of young adolescent girls, who performed better in school and had families with a higher socioeconomic status than the UK average (Boyd et al. 2012). Such biases could have had implications for missing data and associated results. This needs to be kept in mind when interpreting study findings.

3.6.2.4 ALSPAC data

ALSPAC has frequent and detailed waves of data, collected regularly from birth to child age 24 years through questionnaires, clinical measures and biological samples (Fraser et al. 2012; Boyd et al. 2013). Data were collected from the child, parent(s)/primary carer and staff at schools attended by ALSPAC children, with data available for ALSPAC children, ALSPAC mothers/main carer and ALSPAC fathers. This study only focused on child, mother/main carer and father completed questionnaires, alongside child attended clinic data. Table 5 presents the details and number of participants at each wave of child completed questionnaires.

Table 6 presents the details and number of participants at each wave of mother/main carer completed questionnaires.

Table 7 presents the detail and number of participants at each wave of partner completed questionnaires, primarily representing the father of the child.

Table 8 presents the details, number of participants and dates of each Focus clinic attended by ALSPAC children.

71 Table 5: Summary of ALSPAC data collected from child completed questionnaires

Child Completed Questionnaires File Time points N

Your Own Questionnaire CCA1 65 months 7554

My Second Questionnaire CCA2 69 months 7521

Your Next Questionnaire CCA3 73 months 7348

Growing Up CCA4 77 months 7751

My Questionnaire CCA5 81 months 6277

Things to do CCA6 85 months 7426

My Teeth CCB 91 months 7086

Me and My School CCC 97 months 7688

Some more about me CCD 103 months 8223

My World CCE 110 months 8580

My Hands, My Feet & Me CCF 115 months 8084

Rings & Things CCG 122 months 8343

Teeth and Things CCH 128 months 7827

School Life and Me CCJ 134 months 7940

Watches and Funny Feelings CCK 140 months 7544

All Around Me CCL 145 months 7523

Food and Things CCM 157 months 7115

Reading and Singing CCN 157 months 7109

Travelling, Leisure and School CCP 166 months 6877 Boys'/Girls' Experiences, Thoughts

and Behaviour

CCQ 167 months 6160

Life of a Teenager CCR 169 months 6005

Life of a 16+ Teenager CCS 198 months 5131

Your Changing Life CCT 18 years 3372

It's all about you CCU 20 years 4342

Your Life Now YPA 21 years TBC

Life at 22+ YPB 22 years 4026

Me at 23+ YPC 23 years 4233

Year 11 questionnaire for young people

CCXA* 192 months 5439

You and Your Friends CCXB* 192 months 3132

Internet Use CCXC* 17.5 years 1584

Plans and aspirations (DCSF) CCXD* 17.6 years 4500

Gambling CCXE* 17.5 years 3833

You and Your Body CCXF* 19.6 years 1944

*Note – collected in a clinic setting, sent to a subgroup or covered in a single research topic.

72 Table 6: Summary of ALSPAC data collected from mother/main carer completed questionnaires