TEORÍA DE LA VELA

A range of measures of health and health behaviours are available in the GAZEL cohort. Only one measure, sickness absence, was obtained from administrative sources; the rest are self reports. No reliable objective measures of health status were available at the time of commencing the thesis, as is described more fully in section 5.2.8.9 on page 109. Available self-reported measures included: the SF-36 measures of physical and mental functioning, the CES-D depression scale, the Nottingham Health Profile, hearing problems, visual impairment, hospitalization, self-rated health, smoking status and alcohol use. Each health measure is described more fully in the sections below.

5.2.8.1 Short Form 36 Mental and Physical Component Summaries (SF-36 MCS & PCS)

Mental and physical component summary scores from the French standard version of the Short Form 36 Health Survey (SF-36) were used to measure health functioning in 2003 and 2007 (Leplège et al., 2001; Ware Jr and Sherbourne, 1992). The SF-36 questionnaire is an internationally validated measure of health functioning composed of 36 questions about physical and mental functioning which are grouped into eight subscales depicting different health domains. From version 2 of the questionnaire, two summary scores were derived following the standard protocol described in Leplège et al. (2001): a mental component summary score (SF-36 MCS) and a physical component summary score (SF-36 PCS), both ranging from 0–100 with higher scores indicating better health. The variables have acceptable properties for being used as mediating observed variables in structural equation models: SF-36 MCS in 2003 has a skewness of−1.17 and a kurtosis of 4.05; SF-36 PCS in 2003 has a skewness of−1.26 and a kurtosis of 5.09.

5.2.8.2 CES-D depression scale

Depression was defined using a validated French-language version of the CES-D scale (Center for Epidemiologic Studies Depression scale) from the 2005 questionnaire (Führer and Rouillon, 1989). The scale is based on symptoms of depression as seen in clinical cases. However, Radloff (1977) states that the scale is not intended as a clinical diagnostic

tool, rather group averages should be interpreted in terms of levels of symptoms which accompany depression, not in terms of rates of illness.

The questions were reverse-coded when necessary and coded from 0–3 depending on the frequency of occurrence of the symptom, following Radloff (1977). The scores were summed and divided into three categories, designating a lack of symptoms of depression, mild symptoms of depression, and moderate to severe symptoms of depression at the following cut-off points: 0–15, 16–26 and≥27, respectively (Zich et al., 1990).

This is in contrast to the specific cut-offs varying by gender which are usually used in France (Morin et al., 2011), in which the cut-off value for depressed male participants is 17 and for women it is 23 (Führer and Rouillon, 1989). I decided to maintain the same cut-offs for women and men, as having higher cut-off values for women might result in underestimating the prevalence of depressive symptomatology in women (Messing et al., 2003; Van de Velde et al., 2009).

Change in depression. A three-category variable was created, in which depression symptoms improved, stayed the same or worsened.

Individuals were classified as having improving depression symptoms 2005–2009 if they had been classified as having mild or moderate/severe depression symptoms in 2005 and as having insufficient depression symptoms to classify as a case in 2009. In addition, participants who had been classified as having moderate/severe depression symptoms in 2005 who progressed to mild depression symptoms were classified as having improved.

Individuals were classified as having worsening depression symptoms 2005–2009 if they had not originally been defined as a case but subsequently experienced mild or moderate/severe levels of depression symptoms in 2009. Similarly, those who had been classified as having mild depression symptoms in 2005 and progressed to moderate/severe levels of depression symptoms in 2009 were classified as having worsened.

Individuals who did not change category were classified as having levels of depression symptoms that stayed the same.

5.2.8.3 Physical limitations

The Nottingham Health Profile is a measure of general community health. It is available in the GAZEL cohort in the 2006 self-completion questionnaire in a validated French translation (Bucquet et al., 1990). In this thesis, rather than using the Nottingham Health Profile in its full form, a sum scale of physical limitations was created from those items which indicated limitations to physical functioning. These are listed in Appendix A: Table A.8. A trichotomous variable was created: no limitations to physical functioning, one limitation, or two or more limitations. As the data were collected in 2006, the year following the 2005 measurement of quality of life, this variable was used only to compare size effects, as has been done in previous studies (Blane et al., 2004; Demakakos et al., 2010; Netuveli et al., 2006). The Nottingham Health Profile was not used to measure general health because it can suffer from ceiling effects (Falcoz et al., 2002), particularly in healthy cohorts such as the GAZEL cohort, so the SF-36 was used instead.

5.2.8.4 Hearing problems and visual impairment

Participants indicated whether they had hearing problems or a visual impairment in each of the annual self-completion questionnaires. The first appearance of difficulties in hearing or vision in any year was interpreted as the development of hearing problems or a visual impairment. Participants who responded to the rest of a questionnaire but did not indicate a new hearing problem or visual impairment were classified as not having experienced a hearing problem or a visual impairment in that year.

5.2.8.5 Hospitalization

A question about whether participants had been hospitalized in the previous year was included in each annual questionnaire.3 _{Two variables were created. The first variable,}

hospitalization during 2004, was obtained from the 2005 questionnaire from a question which asked whether the participant had been hospitalized during the previous year. The second variable, hospitalization during 2005–2008, describes whether participants reported a hospitalization when filling out any of the questionnaires between January 2006 and January 2009.

Participants who responded to the rest of a questionnaire but did not indicate that any life events had occurred were classified as not having experienced hospitalization in that year. Analyses of responses to other life event questions which could be verified (changes to marital status, retirement) from company records or other parts of the questionnaire suggested that participants were less conscientious in filling out this final section of the questionnaire, which might have weakened any associations between hospitalization and quality of life.

5.2.8.6 Self-rated health

Participants indicated their self-assessed health in the baseline 1989 questionnaire on an A–H scale with polar labelling (very good–very bad). Although this question was asked every year, it is not clear exactly which aspects of health this general, single item measures (Layes et al., 2012; Quesnel–Vallée, 2007), and therefore SF-36 was used instead to indicate general health functioning. Self-rated health in 1989 was used as a continuous auxiliary variable to improve the quality of the full information maximum likelihood estimation.

5.2.8.7 Smoking status

Sample members indicated their smoking status in the 1989 self-completion questionnaire from the following categories: smoker (at least one cigarette per day), non-smoker, ex- smoker (for at least one year). This variable was not included in any analytic models

3_{It is not necessarily straightforward to define hospitalization. However, in the French case, hospital-}

ization is accompanied by a specific charge payable by the patient, the forfait hospitalier, so it is most likely that the GAZEL participants will equate payment of this charge with hospitalization.

but used as a set of dummy auxiliary variables to improve full information maximum likelihood estimation.

5.2.8.8 Alcohol use

A detailed set of questions in the 1989 questionnaire concerned alcohol consumption. Study members indicated how often they consumed each of wine, beer or cider, pastis, whiskey, or other spirits each week, choosing between the categories “never”, “occasionally”, “every day”. If they selected every day, they were asked to indicate the number of glasses of each beverage consumed per day. From this information, a five-category variable of overall alcohol consumption was created: abstainer, occasional, moderate, average and heavy, following Goldberg et al. (2006), as explained in Table 5.1.

Table 5.1: Alcohol consumption categories

Level of

consumption Males Females

Abstainers Never for all alcoholic beverages Never for all alcoholic beverages Occasional No more often than on occasion for any

beverage

No more often than on occasion for any beverage

Moderate No spirits daily. 1–2 glasses of wine, beer or cider daily

No spirits daily. 1 glass of wine, beer or cider daily

Average No spirits daily. 3–4 glasses of wine, beer or cider daily

No spirits daily. 2–3 glasses of wine, beer or cider daily

Heavy Drink spirits daily. 5 or more glasses of wine, beer or cider daily

Drink spirits daily. 4 or more glasses of wine, beer or cider daily

This variable was not included in any analytic models but used as a series of dummy auxiliary variables to improve full information maximum likelihood estimation.

5.2.8.9 Measures of health available in the GAZEL cohort which were not used

The only data available from company physicians’ files are records of height and weight, which are available for a short series in the 1990s for some participants. However, these measurements were not obtained from a standardized protocol. Concerns about data reliability led to these measures not being used in the thesis.

Neither prescription nor medical records were available for use, although participants reported doctor-diagnosed diseases in the annual questionnaires. These reports will likely represent the tip of the clinical iceberg (Last, 1963). The possibility that individuals in a higher social position would be more likely to report illness led to measures of general health functioning being used in this thesis instead of reports of doctor-diagnosed illnesses (Thielen et al., 2009).

Around 3000 participants had undergone medical tests during visits to health screening centres (Léger, 2011; Zins et al., 2009) which might have provided objective health data. However, the small sample and differing collection methods between the 17 centres led to

the data not being suitable for inclusion in this thesis. A second wave of visits to health centres using standardized procedures is being carried out, but the data are being collected too late for inclusion in this thesis.