PMCCPMCCPMCC

Search tips
Search criteria 

Advanced

 
Logo of tobcontTobacco ControlVisit this articleSubmit a manuscriptReceive email alertsContact usBMJ
 
Tob Control. 2007 December; 16(6): 378–383.
PMCID: PMC2807187

Exposure to domestic violence associated with adult smoking in India: a population based study

Abstract

Objective

To investigate the relation between domestic violence and tobacco use among adults in India.

Design

Multilevel cross sectional analyses of a nationally representative population based sample from the 1998–9 Indian national family health survey.

Participants

278 977 individuals aged 15 or older; and 89 092 ever married women aged 15–49.

Main outcome

Dichotomous variables for smoking and chewing tobacco.

Results

Women who reported being abused more than one year ago and those who reported being abused in the past year were more likely to smoke and chew tobacco than women who have never experienced domestic violence. Compared to individuals who lived in homes where no abuse was reported, those who lived in homes where a woman reported experiencing domestic violence were more likely to smoke and chew tobacco.

Conclusion

Domestic violence is associated with higher odds of smoking and chewing tobacco in India. Efforts to control tobacco use need to consider the larger psychosocial circumstances within which individuals who practise such harmful health behaviours reside.

Keywords: smoking, tobacco, domestic violence, stress, India

Tobacco use contributes to the deaths of at least 800 000 people in India every year.1 While smoking is a well established practice among Indian men affecting 29.3% of adult males,2 it is less so for women.3 Although the overall prevalence of smoking among women is low, estimated to be 2.5%,2 there is substantial heterogeneity within the country, with some states observing prevalence rates of up to 24%.4 In addition, the prevalence and the absolute number of female smokers are also anticipated to increase as targeted marketing of cigarettes and social change accompanying rapid economic growth diminish the social norms that have traditionally discouraged smoking by Indian women.1,5 Tobacco use in India is not restricted to smoking, with chewing tobacco representing another main source of tobacco use.1 While there remain marked sex differentials in tobacco chewing,3 the differentials are smaller than those observed for smoking, with current prevalence for tobacco chewing being estimated as 12.0% for women and 28.1% for men.2 Although previous research has documented the socioeconomic and demographic patterning of tobacco use in India,2,6,7,8 there has been little research of the potential psychosocial risk factors that are associated with tobacco use among Indians.

We investigate the relation between domestic violence (DV) and smoking and tobacco chewing in India. We conceptualise DV and exposure to household DV as markers for stressful psychosocial circumstances. Personal experiences of DV or exposure to DV within the home can be regarded as a critical source of psychosocial stress.9,10 According to one estimate, some 40% of Indian women report being slapped, hit, kicked or beaten during their married life,11 suggesting the widespread prevalence of this social risk factor to which women and their families are exposed. Studies conducted in the United States have shown positive associations between DV and smoking,12,13,14,15 and between exposure to household DV and smoking.16 Explanations to account for the association between DV and smoking tend to focus on smoking being a “stress reliever,”17 even though recent evidence on this is mixed.18 It is however clear that, regardless of whether or not smoking reduces stress, smokers and potential smokers believe that it will.19 Indeed, Indians who smoke and chew tobacco frequently identify stress relief as an important reason for initiating and continuing their tobacco use.20,21 We examine the association between experience of DV and current smoking—a marker for psychosocial stress—and tobacco chewing among women, and between exposure to DV within the home and smoking and tobacco chewing among family members, after controlling for a range of demographic and socioeconomic characteristics.

Methods

Data

The analyses used datasets derived from the second National Family Health Survey (NFHS‐2), a nationally representative cross sectional survey administered in India during 1998–9.4 An adult member of each sampled household answered questions about demographic and health information concerning every household member during in‐person interviews with a response rate of 98%. Each household was linked in the data to the primary sampling unit, district, and state in which it was located. The primary sampling units (hereafter called neighbourhoods) were villages or village clusters in rural areas and census enumeration districts in urban areas. After the household members were identified, each ever married woman aged 15–49 in every sampled household answered questions regarding maternal and child health indicators in an in‐person interview, achieving a 96% response rate. The first analytical sample includes the 89 092 women who answered the women's survey and provided complete information on DV victimisation, tobacco use and covariates. The second analytical sample includes the 278 977 family members of these women for whom complete information about tobacco use and covariates was obtained. These participants were sampled in 74 163 households in 3215 neighbourhoods in 440 districts in all 26 Indian states.

Outcomes

Tobacco smoking and chewing were conceptualised as interchangeable manifestations of a stressful social environment. These variables were measured from binary responses given during the household survey.

Exposure

Information regarding DV experience since age 15 recorded in the women's survey yielded a measure of DV recency with the following three categories: never abused, abused more than 12 months ago (past abuse), or abused in the previous 12 months (current abuse). This exposure was used to assess the relation between DV and smoking among the ever married women sample.

Each woman's DV report was additionally linked to her household to create a household DV exposure variable using the same categories. For those households in which more than one woman provided DV information, that of the woman reporting the most recent DV experience was used to represent the household exposure DV. This household variable was used as the exposure in models using the full sample of adult men and women.

Covariates

We considered a range of individual demographic, socioeconomic and behavioural covariates for these analyses (table 11).). Responses to the household questionnaire provided information about the family's religion, caste22 and standard of living.23,24 Other covariates included age, sex, marital status, education, residential living environment, women's employment, pregnancy status and body mass index.

Table thumbnail
Table 1 Descriptive information of the samples

Ethical considerations

Details of this study were approved by the Harvard School of Public Health institutional review board human subjects committee.

Statistical analysis

We utilised a logistic multilevel modelling approach,25,26 and the substantive and technical relevance of these models are well described elsewhere.27,28,29 We modelled the likelihood of being a tobacco smoker or chewer given the fixed effects of own or household abuse reports and the random effects associated with states, districts, neighbourhoods and households. All models were estimated with the quasi‐likelihood approximation with first order Taylor linearisation procedure.25

Results

In the ever married women's sample, 19% of the women reported experiences of abuse with 85% of abused woman reporting abuse by their husband. Substantial associations were found between smoking and past abuse (odds ratio (OR) 1.27, 95% confidence interval CI) 1.10 to 1.46) or current abuse (OR 1.35, 95% CI 1.17 to 1.55) compared to those reporting no abuse (fig 11).). The results in the full sample also indicated a positive association between smoking and living in a household where women reported past abuse (OR 1.27, 95% CI 1.10 to 1.46) or current abuse (OR 1.35, 95% CI 1.17 to 1.55) compared to those living in households where women reported no DV. The association between tobacco chewing and DV in both the woman's sample and the full sample were approximately equivalent to the analogous associations with smoking.

figure tc20651.f1
Figure 1 Odds ratios and confidence intervals for smoking and chewing by own abuse recency in the women's sample and by household abuse recency in the full NFHS. Square represents never abused; diamond represents abuse more than one year ago; ...

We performed several sensitivity analyses to confirm the observed findings. We additionally tested for two and three way interactions between DV and age/SLI/education/caste, and did not observe the interactions to be substantial (results not shown). We also investigated the impact of DV perpetrated by male and female relatives separately in the women's sample and found increased smoking (OR 1.30, 95% CI 1.17 to 1.46) and chewing (OR 1.36, 95% CI 1.28 to 1.44) for those abused by male relatives but not for female relatives (OR 1.07, 95% CI 0.84 to 1.36; OR 1.10, 95% CI 0.97 to 1.26). We further analysed the full sample stratified by age and observed significant associations between smoking/tobacco chewing and DV across all age strata. In additional tests that pertained to specifying fixed effects for the different states, we found that the relation observed between smoking/tobacco chewing and DV did not change, both for the full as well as the ever married women sample. We also re‐estimated the full sample models by excluding women who had been abused and did not find any change in the reported association between smoking or chewing and DV (results not shown). There was some attenuation when abused women and their abusive husbands were removed from the analyses simultaneously, but a substantial association remained between smoking and past household DV (OR 1.12, 95% CI 1.05 to 1.18) or current household DV (OR 1.18, 95% CI 1.11 to 1.25), and between chewing and past household DV (OR 1.11, 95% CI 1.06 to 1.17) or current household DV (OR 1.20, 95% CI 1.15 to 1.26) compared to those living in DV‐free households.

Discussion

Using large, nationally representative samples, we find a strong association between experiencing DV and tobacco use, even after controlling for a range of individual and household level demographic and socioeconomic covariates. We also find that living in households with DV increases the likelihood of tobacco use for all its adult members. The positive association between DV and smoking among women found in this study is the first to be reported for a developing country, and is consistent with those observed in developed countries.12,13,14,15 While some studies have looked at the relation between smoking and exposure to household violence among children,16,30 we believe that this is the first study to investigate this relation among adults.

What accounts for the association between DV and tobacco use? Various explanations have been proposed to justify the role of social context for smoking. Many of these theories focus on aspects of social interaction that include power, physicality, consumption, identity, desire and geography.31 Nonetheless, the majority of the work in this field has focused on DV as a marker of psychosocial stress.12,13,15,32,33,34 It is believed that smoking is associated with elevated levels of stress,17 even though there is considerable debate about the underlying causal mechanisms.18 One plausible explanation is that one or more of the chemical components in tobacco have a pharmacological effect on the metabolic expression of stress in individuals who use tobacco, with the majority of this research focusing on the effects of nicotine. It has been suggested that nicotine may reduce the metabolic expression of stress through an opioid mechanism, by activating a reward pathway such as the mesolymbic dopamine system, or by dampening sympathetic responses to stressful stimuli, although conclusive evidence is still lacking in these areas.35,36,37 In a related vein, increases in mesolimbic dopamine release that result from both stress and nicotine exposure suggest that stress may simply be priming the body to react more favourably to tobacco use, although this hypothesis has never been empirically tested.38,39 Other research has found that smoking serves to reduce immediate stressful feelings, but only in the presence of a distraction, indicating that nicotine may moderate the effect of cognitive attention on stress.40,41 Alternatively, the major role of smoking may be to manage the symptoms of nicotine withdrawal, commonly perceived as stress, since longitudinal studies have found that smoking cessation is followed by a temporary increase in symptoms of stress followed by a reduction of these symptoms to levels below those observed during the baseline period before cessation.42 Since tobacco chewing results in a similar though rather slower uptake in nicotine compared with smoking,43 these nicotine related theories of stress and smoking probably apply to tobacco chewing as well. Regardless of the actual mechanisms, however, there is a widespread belief among smokers in the developed world that tobacco use relieves stress,19 a sentiment that is shared by people in India who smoke or chew tobacco.20,21 This suggests that, apart from any physiological link between smoking and stress, people in India may view tobacco use as a convenient and low cost method for managing symptoms of stress.

The results of this study must also be seen in light of the association between DV and stress. A recent review of studies from the developed world described the increased incidence of stress among women who have been victims of physical violence and indicated that the severity of psychological outcomes increases with an increase in the severity and recency of abuse.9 Studies of women in India and Pakistan have also established an association between DV and poor mental health outcomes among south Asian women.11,44 At the same time, a recent meta‐analysis of 118 studies has shown a strong relation between witnessing domestic violence and behaviours indicating elevated levels of stress in children.10 Taken together, these findings form a plausible link whereby the stress of experiencing DV and being part of a household where DV is active could promote the use of tobacco products.

Limitations

The following caveats need to be considered while evaluating the study findings. The cross sectional design of this study does not allow for the establishment of a causal link from DV to tobacco use. It is possible that the observed relation between DV and tobacco use among women is the result of reverse causation such that a family member's displeasure with a woman's tobacco use leads to abuse.45 It may also be possible that omitted variable bias is responsible for the observed association between DV and tobacco use. For example, it may be that childhood poverty increases the risk of both tobacco use and having a poor dowry, the latter of which has been shown to increase the risk of DV victimisation.46 However, this investigation did control for numerous demographic characteristics, risk factors and key measures of socioeconomic status.

The lack of a clear dose‐response relation between DV and tobacco chewing warrants attention. If experiences of abuse cause a woman to use tobacco, we would expect that current tobacco use would be more strongly related to current abuse than to past abuse. This dose response was not observed for chewing in the women's sample. It could, however, be that a key developmental period for tobacco chewing initiation for women is in late adolescence and young adulthood. Past abuse, which took place during this critical developmental period in a person's life, may indeed be more important in predicting current tobacco use habits than is current abuse. Although longitudinal studies of tobacco chewing among Indian women are conspicuous by their absence, cross sectional research indicates that tobacco chewing initiation continues throughout adulthood and chewing prevalence peaks in the seventh decade of life.6

Use of tobacco smoking and chewing was not self reported, but reported by the respondent to the household survey. If a person had concealed his or her tobacco use from other family members, it may not have been reported during the household survey. Moreover, if DV were more likely to occur in households where other family members know of and disapprove of the woman's tobacco use, this could have biased the results of this study. However, the analysis of the women's sample revealed similar associations between DV and both forms of tobacco use, smoking and chewing, despite the greater social stigma associated with smoking among Indian women.1,47 If the relation between DV and tobacco use resulted solely from abuse occurring when family members discovered and consequently punished a woman for her tobacco use, we would expect the association of DV and smoking, which is highly stigmatised, to be much stronger than that of DV and tobacco chewing, a behaviour associated with much less stigma.

Finally, previous research has shown that domestic violence surveys with multiple behaviourally specific questions tend to elicit more accurate results compared to the global screening questions used in the NFHS.48 This indicates that the rate of domestic violence reported in this study may underestimate that of the general population. Indeed, the 19% lifetime abuse rate reported in this study is substantially lower than the 40% rate reported in a multisite study in India that used multiple questions about many specific types of domestic violence victimisation.11 If under‐reporting of DV were related to tobacco use, this could bias the results of our study. However, in most cases, the person reporting the tobacco use was not the woman who reported her own DV, so any under‐reporting of DV victimisation is likely to be unrelated to the report of tobacco use.

Conclusion

To our knowledge this study is the first to report an association between DV and tobacco use in the context of developing economies, including India. While better study designs, and data collection measures are warranted to understand the connections between DV and smoking, our study provides the basis to consider the importance of widespread psychosocial risk factors as a part of the public health agenda. The results from this study provide information for those working to raise awareness of the harmful health effects of DV, including those that operate by promoting adverse health behaviours. For instance, in a recent study, domestic violence was shown to be associated with asthma in India,49 suggesting the direct part that psychosocial stress may play in the aetiology of that disease. Findings from the current study suggest an indirect role that psychosocial stress may have in increasing poor health outcomes such as asthma, cancer and heart disease via increasing smoking, a known risk factor for these diseases. However, rather than simply viewing psychosocial exposures as risk factors that individuals should be taught to avoid, the strong correlation found in this study between domestic violence and tobacco use suggests policy responses that would consider the power differentials inherent in the dominant social structure.

What this paper adds

  • Personal experiences of domestic violence are associated with higher rates of smoking and chewing tobacco in Indian women
  • Living in households that experience domestic violence is associated with higher rates of smoking and chewing tobacco in India for all its adult members
  • Efforts towards tobacco control need to consider the psychosocial circumstances under which people practise these unhealthy behaviours

Acknowledgements

We acknowledge the support of Macro International (www.measuredhs.com) for providing us access to the 1998–9 Indian National Family Health Survey data. LA is supported by the Harvard Education Program in Cancer Prevention and Control (NIH/NCI 5 R25 CA057711‐12R). SVS is supported by the National Institutes of Health Career Development Award (NHLBI 1 K25 HL081275).

Abbreviations

DV - domestic violence

NFHS - National Family Health Survey

Footnotes

Funding: No direct financial support was available for this study.

Competing interests: SVS as the corresponding author has had full access to all data in the study and has final responsibility for the decision to submit for publication. All of the authors declare that they have no conflicts of interest regarding this manuscript.

Contributors: SVS conceived the study, designed the analysis, and contributed to the interpretation of the results and writing of the manuscript. LA led the analysis, interpretation, and writing of the manuscript. IK, and EB contributed to the interpretation of the results. All authors reviewed and approved the final manuscript.

References

1. Reddy K S, Gupta P C. eds. Report on tobacco control in India. New Delhi: Ministry of Health and Family Welfare, Government of India 2004
2. Rani M, Bonu S, Jha P. et al Tobacco use in India: prevalence and predictors of smoking and chewing in a national cross sectional household survey. Tob Control 2003. 12e4 [PMC free article] [PubMed]
3. Subramanian S V, Nandy S, Kelly M. et al Patterns and distribution of tobacco consumption in India: cross sectional multilevel evidence from the 1998–9 national family health survey. BMJ 2004. 328801–806.806 [PMC free article] [PubMed]
4. IIPS, ORC‐Macro National Family Health Survey, 1998–1999: India. Mumbai: International Institute for Population Sciences, 2000
5. Bansal R, John S, Ling P M. Cigarette advertising in Mumbai, India: targeting different socioeconomic groups, women, and youth. Tob Control 2005. 14201–206.206 [PMC free article] [PubMed]
6. Neufeld K J, Peters D H, Rani M. et al Regular use of alcohol and tobacco in India and its association with age, gender, and poverty. Drug Alcohol Depend 2005. 77283–291.291 [PubMed]
7. Narayan K M, Chadha S L, Hanson R L. et al Prevalence and patterns of smoking in Delhi: cross sectional study. BMJ 1996. 3121576–1579.1579 [PMC free article] [PubMed]
8. Pednekar M, Gupta P, Shukla H. et al Association between tobacco use and body mass index in urban Indian population: implications for public health in India. BMC Public Health 2006. 670 [PMC free article] [PubMed]
9. Briere J, Jordan C E. Violence against women: outcome complexity and implications for assessment and treatment. J Interpers Violence 2004. 191252–1276.1276 [PubMed]
10. Kitzmann K M, Gaylord N K, Holt A R. et al Child witnesses to domestic violence: a meta‐analytic review. J Consult Clin Psychol 2003. 71339–352.352 [PubMed]
11. Kumar S, Jeyaseelan L, Suresh S. et al Domestic violence and its mental health correlates in Indian women. Br J Psychiatry 2005. 18762–67.67 [PubMed]
12. Hathaway J E, Mucci L A, Silverman J G. et al Health status and health care use of Massachusetts women reporting partner abuse. Am J Prev Med 2000. 19302–307.307 [PubMed]
13. Lemon S C, Verhoek‐Oftedahl W, Donnelly E F. Preventive healthcare use, smoking, and alcohol use among Rhode Island women experiencing intimate partner violence. J Womens Health Gend Based Med 2002. 11555–562.562 [PubMed]
14. Verhoek‐Oftedahl W, Pearlman D N, Coutu Babcock J. Improving surveillance of intimate partner violence by use of multiple data sources. Am J Prev Med 2000. 19308–315.315 [PubMed]
15. Vest J R, Catlin T K, Chen J J. et al Multistate analysis of factors associated with intimate partner violence. Am J Prev Med 2002. 22156–164.164 [PubMed]
16. Anda R F, Croft J B, Felitti V J. et al Adverse childhood experiences and smoking during adolescence and adulthood. JAMA 1999. 2821652–1658.1658 [PubMed]
17. Ikard F F, Tomkins S. The experience of affect as a determinant of smoking behavior: a series of validity studies. J Abnorm Psychol 1973. 81172–181.181 [PubMed]
18. Kassel J D, Stroud L R, Paronis C A. Smoking, stress, and negative affect: correlation, causation, and context across stages of smoking. Psychol Bull 2003. 129270–304.304 [PubMed]
19. Baker T B, Brandon T H, Chassin L. Motivational influences on cigarette smoking. Annu Rev Psychol 2004. 55463–491.491 [PubMed]
20. Kotwal A, Thakur R, Seth T. Correlates of tobacco‐use pattern amongst adolescents in two schools of New Delhi, India. Indian J Med Sci 2005. 59243–252.252 [PubMed]
21. Pandey G K, Raut D K, Hazra S. et al Patterns of tobacco use amongst school teachers. Indian J Public Health 2001. 4582–87.87 [PubMed]
22. Subramanian S V, Nandy S, Irving M. et al The mortality divide in India: the differential contributions of gender, caste, and standard of living across the life course. Am J Public Health 2006. 96818–825.825 [PubMed]
23. Filmer D, Pritchett L H. Estimating wealth effects without expenditure data—or tears: an application to educational enrollments in states of India. Demography 2001. 38115–132.132 [PubMed]
24. Rutstein S O, Johnson K. The DHS wealth index: DHS comparative reports 6. Calverton, MD: ORC Macro, 2004
25. Goldstein H. Multilevel statistical models. London: Arnold, 2003
26. Raudenbush S W, Bryk A S. Hierarchical linear models: applications and data analysis methods. 2nd ed. Thousand Oaks, CA: Sage Publications, 2002
27. Blakely T, Subramanian S V. Multilevel studies. In: Oakes JM, Kaufman JS, eds. Methods in social epidemiology. San Francisco: Jossey‐Bass, 2006. 316–340.340
28. Subramanian S V. The relevance of multilevel statistical methods for identifying causal neighborhood effects. Soc Sci Med 2004. 581961–1967.1967 [PubMed]
29. Subramanian S V, Jones K, Duncan C. Multilevel methods for public health research. In: Kawachi I, Berkman LF, eds. Neighborhoods and health. New York: Oxford University Press, 2003. 65–111.111
30. Dube S R, Felitti V J, Dong M. et al The impact of adverse childhood experiences on health problems: evidence from four birth cohorts dating back to 1900. Prev Med 2003. 37268–277.277 [PubMed]
31. Poland B, Frohlich K, Haines R J. et al The social context of smoking: the next frontier in tobacco control? Tob Control 2006. 1559–63.63 [PMC free article] [PubMed]
32. Bullock L F, Mears J L, Woodcock C. et al Retrospective study of the association of stress and smoking during pregnancy in rural women. Addict Behav 2001. 26405–413.413 [PubMed]
33. McFarlane J, Parker B, Soeken K. Physical abuse, smoking, and substance use during pregnancy: prevalence, interrelationships, and effects on birth weight. J Obstet Gynecol Neonatal Nurs 1996. 25313–320.320 [PubMed]
34. Weaver T L, Etzel J C. Smoking patterns, symptoms of PTSD and depression: preliminary findings from a sample of severely battered women. Addict Behav 2003. 281665–1679.1679 [PubMed]
35. Dani J A, Heinemann S. Molecular and cellular aspects of nicotine abuse. Neuron 1996. 16905–908.908 [PubMed]
36. Pomerleau O F. Endogenous opioids and smoking: a review of progress and problems. Psychoneuroendocrinology 1998. 23115–130.130 [PubMed]
37. Pomerleau O F, Pomerleau C S. Research on stress and smoking: progress and problems. Br J Addict 1991. 86599–603.603 [PubMed]
38. Olausson P, Engel J A, Soderpalm B. Behavioral sensitization to nicotine is associated with behavioral disinhibition; counteraction by citalopram. Psychopharmacology (Berl) 1999. 142111–119.119 [PubMed]
39. Panagis G, Nisell M, Nomikos G G. et al Nicotine injections into the ventral tegmental area increase locomotion and Fos‐like immunoreactivity in the nucleus accumbens of the rat. Brain Res 1996. 730133–142.142 [PubMed]
40. Kassel J D, Shiffman S. Attentional mediation of cigarette smoking's effect on anxiety. Health Psychol 1997. 16359–368.368 [PubMed]
41. Kassel J D, Unrod M. Smoking, anxiety, and attention: support for the role of nicotine in attentionally mediated anxiolysis. J Abnorm Psychol 2000. 109161–166.166 [PubMed]
42. Parrott A C. Does cigarette smoking cause stress? Am Psychol 1999. 54817–820.820 [PubMed]
43. Pitsiu M, Gries J M, Benowitz N. et al Modeling nicotine arterial‐venous differences to predict arterial concentrations and input based on venous measurements: application to smokeless tobacco and nicotine gum. J Pharmacokinet Pharmacodyn 2002. 29383–402.402 [PubMed]
44. Fikree F F, Bhatti L I. Domestic violence and health of Pakistani women. Int J Gynaecol Obstet 1999. 65195–201.201 [PubMed]
45. Martin S L, Beaumont J L, Kupper L L. Substance use before and during pregnancy: links to intimate partner violence. Am J Drug Alcohol Abuse 2003. 29599–617.617 [PubMed]
46. Rao V. Wife‐beating in rural south India: a qualitative and econometric analysis. Soc Sci Med 1997. 441169–1180.1180 [PubMed]
47. Gupta P C, Ray C S. Smokeless tobacco and health in India and South Asia. Respirology 2003. 8419–431.431 [PubMed]
48. Ellsberg M, Heise L, Pena R. et al Researching domestic violence against women: methodological and ethical considerations. Stud Fam Plann 2001. 321–16.16 [PubMed]
49. Subramanian S V, Ackerson L K, Subramanyam M A. et al Domestic violence is associated with adult and childhood asthma prevalence in India. Int J Epidemiol 2007. 36569–579.579 [PubMed]

Articles from Tobacco Control are provided here courtesy of BMJ Publishing Group