Diverging destinies: ‘social’ data within the TwinsUK cohort

Background: Twins offer social scientists a unique opportunity to understand the interplay of social factors and physical and mental well-being. TwinsUK is the largest UK registry of adult mono- and dy-zygotic twins, but most of the research that utilises the cohorts’ data to date has focused on the genetic underpinnings of complex disease. Methods: Following formal unstructured discussions with social scientists we identified key areas of research interest and annotated the historical data collections in TwinsUK where they could be applied to these research aims. Results: We present a summary of variables identified as of key interest to researchers from the social science sphere, spanning the following domains: 1: Parenting, child rearing and pregnancies; 2: Working habits and patterns; 3: Sleeping habits and patterns; 4: Social support; 5: Negative life events; 6: Spousal relationships. Conclusions: TwinsUK has a wide range of genetic and health data that would allow investigation of research questions focusing on these domains.


Introduction
Twin studies enable researchers to disentangle and quantify the influences of relative contributions of genetic and early-life environmental factors to the variability of a trait.Twins therefore provide a unique opportunity to understand the interplay of social factors and physical and mental health and well-being, and can offer social scientists a 'natural experiment' where randomised controlled studies would otherwise be impossible or unethical 1 .Using a classical MZ-DZ comparison, researchers can compare outcomes between twin-pairs who are discordant on an exposure of interest 2 .Where there is within-pair discordance, this provides a unique tool to identify the contributing biological and environmental factors, and how these factors may alter health across the life course and diverge one twin's health trajectory from the other (a 'diverging destiny').
TwinsUK is a cohort of ~14,000 volunteer adult twins.Thanks to an extensive engagement strategy and highly responsive twins, of the 69% of registered twins who have completed an in-person clinical assessment, approximately half have completed at least two follow-on visits.Consequently, extensive longitudinal data are available spanning more than 25 years in some instances.The age range of active twins is 18 -100; the median age however is 60, meaning the cohort is particularly well-positioned for understanding the accumulation of life course exposures and age-related disease 3 .Thus far, the TwinsUK data have been used primarily to understand the genetic basis of complex disease, leaving underutilized the extensive data capturing twins' 'social' exposures as a resource to answer questions crucial to social scientists.
Here, we present a summary of the key social variables within our cohort collected prior to 2020, and the extent of twin pair discordance on each variable.Variables were identified as of key interest to researchers based on research areas in the social sciences.

Ethical approval and consent
The data which has been generated and provided in the report has been collected via questionnaires that had received ethical approval associated with TwinsUK Biobank (19/NW/0187), Twins UK (EC04/015) or Healthy Ageing Twin Study (H.A.T.S) (07/H0802/84) studies from NHS Research Ethics Committees at the Department of Twin Research and Genetic Epidemiology, King's College London.All members of the study hold the right to withdraw their consent and data partially or entirely upon their request.Upon joining TwinsUK, participants complete a written or online consent form to take part in subsequent research.Currently this takes place upon registration with TwinsUK, and historically this took place upon an individual's first participation in a study or attendance of a clinic visit.TwinsUK members do not subsequently sign consent for every individual questionnaire, but they are free to choose not to complete individual questionnaires, and consent is implied when participants return their responses.TwinsUK members must be able to give consent; if the ability to consent is impaired, they are not able to join TwinsUK.TwinsUK members who wish to change their participation status with TwinsUK can do so at any time by contacting the team on email or via phone and quoting their TwinsUK participant study number.Participants are additionally able to change whether they are invited to studies and the communications they receive.TwinsUK members may also request for their data and/or samples to be destroyed at any time.Participants in questionnaires can skip questions and are not obliged to answer.Questionnaires and studies are discussed with the Twin Voluntary Advisory Panel, consisting of participants of the twin cohort, prior to implementation.

The TwinsUK cohort
The Department of Twin Research and Genetic Epidemiology at St. Thomas' Hospital, King's College London (KCL), hosts the UK's largest adult twin registry (or TwinsUK).The registry was initially set up to investigate osteoporosis and osteoarthritis, and the success of these initial studies allowed the cohort to expand, operating with rolling recruitment for new pairs aged over 18.Further details of the history of the cohort are detailed in Verdi et al., 2019 3 .The adult participants consist of 14,575 monozygotic (MZ) and dizygotic (DZ) twins aged between 18 to 100 years.Since 1992, active twins have participated in both questionnaire and clinical visits, where multiple samples and physical measures were obtained, resulting in extensive health and multiomics data (further detail of the visits is outlined in 3,4).

Data collection
Much of the data presented here is derived from questionnaire-based collection covering a broad range of health-related topics (e.g.co-morbidities, dietary information).Core questionnaires are collected on a rolling basis and supplemented with one-off questionnaires depending on research need.Core questionnaires are posted to individuals and returned either in person at a clinical visit or posted back.Other questionnaires (such as the first of our Covid questionnaires, as described by Suthahar et al. 2021 5 ) are also posted, emailed, or collected over the phone.Where electronic questionnaires are used, Qualtrics is used to collect the data; paper questionnaire data has been processed by Abacus Data and Mailing Ltd since 2011.Some of the summaries presented below are from questionnaires that may have included eligibility criteria/been targeted at a specific subset -further details of the specific per questionnaire protocol are available from the TwinsUK data team.

Protocol to generate this dataset
Below, we present key domains of interest to researchers seeking to understand and disentangle the genetic and environmental influence on biosocial phenotypes.Following formal unstructured discussions with social scientists we identified key areas of research interest and annotated the historical data collections in TwinsUK where they could be applied to these research aims.The domains are intended as a comprehensive, but not exhaustive, overview of pre-2020 social data within the TwinsUK cohort.A multitude of other measures are available in the cohort (see data availability) and researchers may also be interested in the longitudinal data captured by COVID-19 Personal Experience study 5 .
For each identified domain, the relevant questions within the dataset are summarised below, including the relevant question code to expedite data requests, the question phrasing, the number of respondents per code (including 'duplicate' responders -where an individual may have responded to the questionnaire more than once, usually at a different date), the average and range of response year and relevant summary statistics.Some minimal data cleaning has been applied (e.g.removing responses not in possible range) but researchers should be aware that values may change slightly where they apply different filtering.All data cleaning and analysis was undertaken in R version 3.6.3and RStudio version 1.1.423.
The strength of twins' data is the ability to disentangle genetic and environmental influences on phenotypes.Therefore, of use to researchers in designing a study is understanding of the discordance, or number of twins who differ from their co-twin for a phenotype.We therefore present a measure of discordance as follows:

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For continuous variables, discordance between twin pairs was considered as a difference of a greater than one standard deviation of a twin from their co-twin.

•
For discrete/ordinal variables, twins were considered discordant where the difference in categories was greater than one between a twin and their co-twin.

•
For binary variables, twins were considered as discordant where answers were different from their co-twins.
The number of twins who had both answered the question of interest was calculated by mapping the pairs and removing any where one individual had not answered or was missing data.
The reasons data could be missing from one twin are generally because the twin skipped a question, and rare cases because of a recording error or the co-twin is deceased or no longer a cohort participant.Discordance was calculated as time invariant (i.e.differing time of response between twins was not considered, although the majority of responses were recorded at similar times).

Results
We identified six social domains within TwinsUK data pre-dating 2020, with 21 subdomains, as follows:  3A) 3B Trouble sleeping and insomnia (Table 3B) 3C Daytime sleepiness and fatigue (Table 3C) 3D Sleeping drugs (Table 3D) 3E Hours sleeping (Table 3E) Domain 4: Social support 4A Coping with stressful events (Table 4A) Domain 5: Negative life events 5A Major life events -past five years (Table 5A) 5B Major life events -past ten years (Table 5B) 5C Sudden death family member (Table 5C) 5D Ever been widowed (Table 5D) 5E History of abuse (Table 5E) Domain 6: Spousal relationships 6A Current marital/relationship status (Table 6A) 6B Marriage history: divorce (Table 6B) 6C Age when first married (Table 6C) 6D Ever been married (Table 6D) 6E Length of relationships (Table 6E) The questions making up each domain were from questionnaires spanning between 1997 -2018, and will reflect a mix of selected and unselected subsets of TwinsUK cohort (for detailed cohort description, see Verdi et al., 2019 3 ).

Domain 1: Parenting, child rearing and pregnancies
TwinsUK participants reported having an average of two children (Table 1A), with a relatively stable rate of discordance across the years of questionnaire collection (approximately 55% of pairs, apart from the earliest data collection where the rate of discordance was 64.8%).Nearly three-quarters of the cohort have had children (Table 1B) and the mean age across the measures for age of first pregnancy was 26 (Table 1C).

Domain 2: Working habits and patterns
The average number of years spent without employment within the cohort was 9.9 (Table 2A); with the average length of years spent working in part time work being 11.1 years (Table 2B).Nearly half of respondents (45.2%) had worked in a fulltime care giving role (Table 2C).The average working hours per week reported was 31.7, but this was highly variable (SD=12.9,Table 2D).

Domain 3: Sleeping habits and patterns
Over 1,000 twin pairs were discordant for their sleep quality at time of response (Table 3Ai) although many (75.5%) reported they had a regular sleeping pattern during the working week (Table 3Aii).Most participants reported slight levels of insomnia (Table 3B) and daytime sleepiness and fatigue (Table 3C).15.5% and 6.6% of responders reported use of non-prescription and prescription sleeping medications respectively (Table 3D).The average hours slept per night was between 7-8 hours (Table 3E).

Domain 4: Social support
Over 60% of responding twin pairs were discordant for their ability to get emotional support from others and handling difficult situations without needing emotional support from others (Table 4A).

Domain 5: Negative life events
Over half (54.9%) of responders reported that they had experienced a self-defined major negative life event related to their home and family in the five years prior to questionnaire (Table 5Ai); events related to home and family were also the most stressful (Table 5Aii).Comparatively lower rates of major life events were reported in ten years prior to questionnaire (Table 5Bi) but with similar stress levels (Table 5Bii).Fathers were more likely to have been reported as dying suddenly (13.5%) than other family members (Table 5C).In 2013, 22.9%

Table 5Aii. Major life events -past 5 years ii (stress level). Summary of responses for TwinsUK participants in response to question:
For each event that you experienced [as in 5Ai] please rate how stressful it was on a scale 0 to 10 where 0 = "not at all stressful" and 10 = "extremely stressful".   of responders reported being widowed; of the 398 twin pairs responding 26% (n=104) were discordant (Table 5D).Reports of childhood abuse was 6.3-6.7% with within pair discordance ranging between 9.7-12% of responding pairs (Table 5E).

Domain 6: Spousal relationships
The majority (72-76%) of participants reported being married or in a relationship at time of questionnaire (Table 6Ai-Table 6Aii), with divorce rates between 20-36.2% of responders depending Table 5Bii.Major life events -past 10 years ii (stress level).Summary of responses for TwinsUK participants in response to question: For each event that you experienced [as in 5Bi] please rate how stressful it was on a scale 0 to 10 where 0 = "not at all stressful" and 10 = "extremely stressful".5B6.(Q10_34) Major events with your Health, 5B7.(Q10_38) Major events in your Home and Family, 5B8.
(Q10_42) Major events with your Work, 5B9 (Q10_46) Major events in your Interpersonal Life, %F = % female responses, SD = standard deviation, N twin pairs = Number of twin pairs where both responded, %MZ = percentage of responding twin pairs who are mono-zygotic (identical) twins, %D = % of responding twin pairs considered discordant, %MZD = percentage of discordant twin pairs who are monozygotic.on the year/questionnaire (Table 6Bi), and the mean number of times married was 1.2 (Table 6Bii).The mean age of first marriage was 24.3 years with a 22.8% rate of discordance (Table 6C).88.9% responders reported that they had ever been married (Table 6D) with the average length of relationship with current partner 30 years (Table 6E).

Limitations of data
Not all the participants here will have longitudinal and/or multi-omics data, and therefore the specific numbers available to interested parties will differ dependent on the research question.

Open Peer Review
Current Peer Review Status:

Margot P van de Weijer
Psychiatry, Amsterdam University Medical Centres, Amsterdam, North Holland, The Netherlands I believe this paper provides a useful summary of the social data present in the TwinsUK dataset, which will be helpful for (twin) researchers when considering to use TwinsUK data.I have two minor comments, both with respect to where I believe the paper would benefit from more details: The first paragraph of the introduction very briefly mentions how twin data can be used as a sort of "natural experiment" when you have discordant twin pairs.I think the rationale behind this is clear for twin researchers, but I imagine quite vague for others not as familiar with twin research.It think it would benefit the paper if the authors would elaborate some more on how and why (discordant) twin data can be used. 1.
The limitations section only mentions that not all participants will have longitudinal or omics data, but I imagine there might be some other limitations with respect to the data's representativeness? 2.

Is the rationale for creating the dataset(s) clearly described? Yes
Are the protocols appropriate and is the work technically sound?Yes

Are sufficient details of methods and materials provided to allow replication by others? Yes
Are the datasets clearly presented in a useable and accessible format?Yes Competing Interests: No competing interests were disclosed.
Mention that comparing MZ twins only is kind of a silver bullet for causal inference.2.
It would be helpful to have in addition information about age distribution (e.g., age brackets with respective n of cases).I know that there are some decisions to make how to cope with different measurement time points, but an aggregate information would be enough.

3.
Some information about selectivity when including social information in addition to health would be interesting (representativeness of the data), but this is less urgent.

Are the datasets clearly presented in a useable and accessible format? Yes
Competing Interests: No competing interests were disclosed.
Reviewer Expertise: social stratification, behavioural genetics, organizational inequalities, work-life 5A6. (Q10_34) Major events with your Health 5A7.(Q10_38) Major events in your Home and Family 5A8.(Q10_42) Major events with your Work, 5A9.(Q10_46) Major events in your Interpersonal Life, %F = % female responses, SD = standard deviation, N twin pairs = Number of twin pairs where both responded, %MZ = percentage of responding twin pairs who are mono-zygotic (identical) twins, %D = % of responding twin pairs considered discordant.Discordance and twin pairs consider all responders to 5Ai, not just affirmative responses, %MZD = percentage of discordant twin pairs who are mono-zygotic.

Version 1 Reviewer
Report 06 October 2023 https://doi.org/10.21956/wellcomeopenres.18932.r66883© 2023 van de Weijer M. This is an open access peer review report distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Table 1A . Number of children. Summary
of responses for TwinsUK participants in response to questions: 1A1.(P003144) Number of children, 1A2.(P010448) Number of children, 1A3.(Q10_158) 'Please write in the number of [biological children] you have had in your family', 1A4.(PH0000798) 'How many pregnancies have you had resulting in a live birth?' %F = % female responses, SD =standard deviation, %MZ = percentage of responding twin pairs who are mono-zygotic (identical) twins, N twin pairs = Number of twin pairs where both responded, %D = % of responding twin pairs considered discordant, %MZD = percentage of discordant twin pairs who are mono-zygotic.

Table 1C. Age at pregnancy of first child. Summary of responses for TwinsUK participants in response to questions: 1C1. (P002891) Year of birth of child 1*; 1C2. (P000942) Give in birth order, including still born and premature babies that died soon after being born, your children
's year of birth (Child 1)*; 1C3.(Q10_163) Please give, in birth order, (including stillbirth or premature babies that died soon after being born) your biological children's sex, year of birth, and if applicable, year of death.Response option: Child 1, birth*; 1C4.(PH0001201) 'How old were you when you had your first baby?' %F = % female responses, SD = standard deviation, N twin pairs = Number of twin pairs where both responded, %MZ = percentage of responding twin pairs who are mono-zygotic (identical) twins, %D = % of responding twin pairs considered discordant, %MZD = percentage of discordant twin pairs who are mono-zygotic.*Age calculated as difference between birth year of child and participants birth year.

Table 2A .
History of unemployment.Summary of responses for TwinsUK participants in response to question: 2A1.(Q11A_44) 'In your life, since turning 16 years old, approx.how many years altogether have you spent working without employment?' %F = % female responses, SD = standard deviation, N twin pairs = Number of twin pairs where both responded, %MZ = percentage of responding twin pairs who are mono-zygotic (identical) twins, %D = % of responding twin pairs considered discordant, %MZD = percentage of discordant twin pairs who are mono-zygotic.

Table 2B
. Part time work.Summary of responses for TwinsUK participants in response to question: 2B1.(Q11A_43) 'In your life, since turning 16 years old, approx.how many years altogether have you spent working in part-time employment?' %F = % female responses, SD = standard deviation, N twin pairs = Number of twin pairs where both responded, %MZ = percentage of responding twin pairs who are mono-zygotic (identical) twins, %D = % of responding twin pairs considered discordant, %MZD = percentage of discordant twin pairs who are mono-zygotic.

Table 2Ci . Full time care giving role and housework
. i. Summary of responses for TwinsUK participants in response to question: 2C1.(Q11A_72) Have you ever worked in the following areas and/or capacities: housewife / full-time parent / carer?%F = % female responses, %Yes = % yes response, N twin pairs = Number of twin pairs where both responded, %MZ = percentage of responding twin pairs who are mono-zygotic (identical) twins, %D = % of responding twin pairs considered discordant, %MZD = percentage of discordant twin pairs who are mono-zygotic.

Table 2Cii . Full time care giving role and housework ii.
Summary of responses for TwinsUK participants in response to question: 2C2.(Q17D_28) During the last week, how many hours did you spend on each of the following physical activities: Housework/Childcare/ Carer?%F = % female responses, SD =standard deviation, N twin pairs = Number of twin pairs where both responded, %MZ = percentage of responding twin pairs who are mono-zygotic (identical) twins, %D = % of responding twin pairs considered discordant, %MZD = percentage of discordant twin pairs who are mono-zygotic.

Table 3Ai . Sleep quality and patterns
i. Summary of responses for TwinsUK participants in response to question: How would you describe your sleep quality over the last month?With the following response options: 1. Very poor, 2. Poor, 3. Satisfactory, 4. Good, 5. Very good.%F = % female responses, SD = standard deviation, N twin pairs = Number of twin pairs where both responded, %MZ = percentage of responding twin pairs who are mono-zygotic (identical) twins, %D = % of responding twin pairs considered discordant, %MZD = percentage of discordant twin pairs who are mono-zygotic.

Table 3Aii . Sleep quality and patterns ii
. Summary of responses for TwinsUK participants in response to question: Do you have a regular sleep pattern during the working week?%F = % female responses, %Yes = % yes response, N twin pairs = Number of twin pairs where both responded, %MZ = percentage of responding twin pairs who are mono-zygotic (identical) twins, %D = % of responding twin pairs considered discordant, %MZD = percentage of discordant twin pairs who are mono-zygotic.

Table 2D .
Working hours per week.Summary of responses for TwinsUK participants in response to question: 2D1 (Q2_289) How many hours per week do you usually work in your job/business?Please exclude meal breaks and paid overtime.%F = % female responses, SD = standard deviation, N twin pairs = Number of twin pairs where both responded, %MZ = percentage of responding twin pairs who are mono-zygotic (identical) twins, %D = % of responding twin pairs considered discordant, %MZD = percentage of discordant twin pairs who are mono-zygotic.

Table 3B .
Trouble sleeping and insomnia.Summary of responses for TwinsUK participants in response to question: 3B1.(P001470) 'Have you recently had difficulty in staying asleep once you are off?'With the following response options: 0: Not at all, 1: No more than usual, 2: Rather more than usual, 3: Much more than usual 3B2.(P001469) 'Have you recently lost much sleep over worry?'With the following response options: 0: Not at all, 1: No more than usual, 2: Rather more than usual, 3: Much more than usual; 3B3.(Q4_23) 'How often did you have insomnia (trouble sleeping) in the last year?'With the following response options: 0: Does not occur or less than once a month, 1: Occurs about once a month, 2: Occurs about once a week, 3: Occurs several times a week, 4: Occurs daily; 3B4.(Q4_24) 'How much did the insomnia (trouble sleeping) bother you in the last year?'With the following response options: 0: Not a problem, 1: It bothers me slightly, 2: It bothers me moderately, 3: It bothers me severely, 4: It bothers me extremely.%F = % female responses, SD = standard deviation, N twin pairs = Number of twin pairs where both responded, %MZ = percentage of responding twin pairs who are mono-zygotic (identical) twins, %D = % of responding twin pairs considered discordant, %MZD = percentage of discordant twin pairs who are mono-zygotic.

Table 3C . Daytime sleepiness and fatigue
. Summary of responses for TwinsUK participants in response to question: 3C1.(Q4_25) 'How often did you get fatigue (tiredness) in the last year?'With the following response options: 0: Does not occur or less than once a month, 1: Occurs about once a month, 2: Occurs about once a week, 3: Occurs several times a week, 4: Occurs daily; 3C2.(Q4_26) 'How much did fatigue (tiredness) bother you in the last year?' 0: Not a problem, 1: It bothers me slightly, 2: It bothers me moderately, 3: It bothers me severely, 4: It bothers me extremely; 3C3.(Q2_74) 'How often, if at all, do you experience sleepiness during the daytime?'With the following responses: 1: Never, 2: Rarely, 3: Sometimes, 4: Frequently, 5: Always; 3C4.(Q11A_159) 'How often, if at all, do you experience sleepiness in the daytime?'With the following responses: 1: Never, 2: Rarely, 3: Sometimes, 4: Frequently, 5: Always.%F = % female responses, SD = standard deviation, N twin pairs = Number of twin pairs where both responded, %MZ = percentage of responding twin pairs who are mono-zygotic (identical) twins, %D = % of responding twin pairs considered discordant, %MZD = percentage of discordant twin pairs who are mono-zygotic.

Table 3D .
Use of sleeping drugs.Summary of responses for TwinsUK participants in response to question: 3D1 (Q11B_207) 'Have you ever taken this drug: Sleeping tablets?; 3D2 (Q11B_30) 'Have you ever taken this drug every day for over a month: Sleeping tablets / tranquilisers?' %F = % female responses, %Yes = % yes response, SD = standard deviation, N twin pairs = Number of twin pairs where both responded, %MZ = percentage of responding twin pairs who are mono-zygotic (identical) twins, %D = % of responding twin pairs considered discordant, %MZD = percentage of discordant twin pairs who are mono-zygotic.

Table 3E .
Hours sleeping.Summary of responses for TwinsUK participants in response to question: 3E1 (Q7_16) 'On average, how many hours per night do you sleep during a working week (Sun-Thru night)?' with the following possible responses: 1: Less than 6 hours, 2: *2 individuals removed for stating greater than 24 hours Table 4A.Social support.Summary of responses for TwinsUK participants in response to question: 4A1.(Q9_144) 'Please indicate what you generally do and feel when you experience stressful events.-I get emotional support from others.'With possible responses: 1: I usually don't do this at all, 2: I usually do this a little bit, 3: I usually do this a medium amount, 4: I usually do this a lot, 4A2.(Q16_145) 'Please read each statement and tick the box that best reflects your degree of agreement or disagreement with that statement -I can handle difficult situations without needing emotional support from anyone else.'With possibly responses: 1: Strongly Agree, 2: Agree, 3: Neutral (neither agree or disagree), 4: Disagree, 5: Strongly Disagree.%Yes = % yes response, %F = % female responses, SD = standard deviation, %MZ = percentage of responding twin pairs who are mono-zygotic (identical) twins, N twin pairs = Number of twin pairs where both responded, %D = % of responding twin pairs considered discordant, %MZD = percentage of discordant twin pairs who are mono-zygotic.

Table 5Ai . Major life events -past 5 years.
Summary of responses for TwinsUK participants in response to question: Please indicate whether you have experienced any major events in any of the following areas of your life during the past 5 years (2000-2005): 5A1.(Q10_ 33) Major events with your Health, 5A2.(Q10_37) Major events in your Home and Family, 5A3.(Q10_41) Major events with your Work, 5A4.(Q10_45) Major events in your Interpersonal Life, 5A5.(Q10_49)Major Economic or Legal event.%Yes = % yes response, %F = % female responses, SD = standard deviation, N twin pairs = Number of twin pairs where both responded, %MZ = percentage of responding twin pairs who are mono-zygotic (identical) twins, %D = % of responding twin pairs considered discordant, %MZD = percentage of discordant twin pairs who are mono-zygotic.

Table 5Bi . Major life events -past 10 years i.
Summary of responses for TwinsUK participants in response to question: Please indicate whether you have experienced any major events in any of the following areas of your life between 5 and 10 years ago (1995-1999): 5B1.(Q10_33)Major events with your Health, 5B2.(Q10_37) Major events in your Home and Family, 5B3.(Q10_41) Major events with your Work, 5B4.(Q10_45) Major events in your Interpersonal Life, 5B5.(Q10_49) Major Economic or Legal event.%Yes = % yes response, %F = % female responses, SD = standard deviation, N twin pairs = Number of twin pairs where both responded, %MZ = percentage of responding twin pairs who are mono-zygotic (identical) twins, %D = % of responding twin pairs considered discordant, %MZD = percentage of discordant twin pairs who are mono-zygotic.

Table 5C .
Sudden death of a family member.Summary of responses for TwinsUK participants in response to question: 5C1.(P003093) Is there anyone in your family who died suddenly?-response option: Mother.5C2.(P003094) Is there anyone in your family who died suddenly?-response option: Father.5C3.(P003095) Is there anyone in your family who died suddenly?-response option: any sister.5C4.(P003096) Is there anyone in your family who died suddenly?-response option: any brother.5C5.(P003097) Is there anyone in your family who died suddenly?-response option: any child.%Yes = % yes response, %F = % female responses, SD = standard deviation, N twin pairs = Number of twin pairs where both responded, %MZ = percentage of responding twin pairs who are mono-zygotic (identical) twins, %D = % of responding twin pairs considered discordant, %MZD = percentage of discordant twin pairs who are mono-zygotic.

Table 5D .
Ever been widowed.Summary of responses for TwinsUK participants in response to question: 5D1.(Q11A_35) Have you ever been widowed?5D2.(Q17D_10) In the past ten years were you widowed?5C3.(PH0001333) What is your current relationship status? -response option: widowed.%Yes = % yes response, %F = % female responses, SD = standard deviation, , N twin pairs = Number of twin pairs where both responded, %MZ = percentage of responding twin pairs who are mono-zygotic (identical) twins, %D = % of responding twin pairs considered discordant, %MZD = percentage of discordant twin pairs who are mono-zygotic.

Table 5E . History of abuse.
Summary of responses for TwinsUK participants in response to question: 5E1.(Q10_227) As a child, were you ever a victim of physical or sexual abuse?(As this may be linked to some medical conditions.)-response option: physical abuse 5E2.(Q10_228) As a child, were you ever a victim of physical or sexual abuse?(As this may be linked to some medical conditions.)-response option: sexual abuse %Yes = % yes response, %F = % female responses, SD = standard deviation, N twin pairs = Number of twin pairs where both responded, %MZ = percentage of responding twin pairs who are mono-zygotic (identical) twins, %D = % of responding twin pairs considered discordant, %MZD = percentage of discordant twin pairs who are mono-zygotic.

Table 6Ai .
Current Marital/Relationship status i. Summary of responses for TwinsUK participants in response to question: 6A1.(Q11A_30) Are you currently married?, 6A2.(Q11A_31) Are you currently separated from your spouse although not divorced?6A3.(Q14_4) Are you currently in a relationship?, 6A4 (Q17D_5) Are you currently in a relationship?, 6A5 (Q17D_7) Is your relationship status different from ten years ago?, 6A6 (PH0001326) What is your current relationship status? -response option: Single, not seeing anyone.6A7 (PH0001327) What is your current relationship status? -response option: Single, but dating someone.6A8.(PH0001330) What is your current relationship status? -response option: Married.6A9 (PH0001331) What is your current relationship status? -response option: Separated.6A10 (PH0001332) What is your current relationship status? -response option: Divorced.6A11.(PH0001334) Are you currently married or in a relationship?%Yes = % yes response, %F = % female responses, SD = standard deviation, N twin pairs = Number of twin pairs where both responded, %MZ = percentage of responding twin pairs who are mono-zygotic (identical) twins, %D = % of responding twin pairs considered discordant, %MZD = percentage of discordant twin pairs who are mono-zygotic.

Table 6Aii . Current Marital/Relationship status ii. Summary
Widowed (6).%F = % female responses, SD = standard deviation, N twin pairs = Number of twin pairs where both responded, %MZ = percentage of responding twin pairs who are mono-zygotic (identical) twins, %D = % of responding twin pairs considered discordant, %MZD = percentage of discordant twin pairs who are mono-zygotic.

Table 6E .
Length of relationship.Summary of responses for TwinsUK participants in response to question: 6E1 (PH0001335) 'How long have you been together with your current partner?(Years') %F = % female responses, SD = standard deviation, N twin pairs = Number of twin pairs where both responded, %MZ = percentage of responding twin pairs who are mono-zygotic (identical) twins, %D = % of responding twin pairs considered discordant, %MZD = percentage of discordant twin pairs who are mono-zygotic.