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Widening inequalities in self-rated health by material deprivation? A trend analysis between 2001 and 2011 in Germany
  1. Timo-Kolja Pförtner1,
  2. Frank J Elgar2
  1. 1Faculty of Human Sciences and Faculty of Medicine, Institute of Medical Sociology, Health Services Research, and Rehabilitation Science, University of Cologne, Cologne, Germany
  2. 2Institute for Health and Social Policy and Douglas Mental Health University Institute, McGill University, Montreal, Quebec, Canada
  1. Correspondence to Dr Timo-Kolja Pförtner, Faculty of Human Sciences and Faculty of Medicine, Institute of Medical Sociology, Health Services Research, and Rehabilitation Science (IMVR), University of Cologne, Eupener Str. 129 Cologne 50933, Germany; timo-kolja.pfoertner{at}uk-koeln.de

Abstract

Background Research on inequalities in health has shown a strong association between the lack of standard of living (defined as material deprivation) and self-rated health (SRH). In this study, we sought to further examine this association in a trend analysis of relative and absolute inequalities in SRH as defined by material deprivation in Germany.

Methods Data were obtained from the German Socio-Economic Panel (GSOEP) between 2001 and 2011. Material deprivation was measured on the basis of 11 living standard items missing due to financial reasons. We used the relative index of inequality (RII) and slope index of inequality (SII) to measure inequalities in SRH by material deprivation, calculating pooled interval logistic regression with robust SEs. Stepwise models were estimated, including demographic and socioeconomic variables, to assess their inter-relation with inequalities in SRH by material deprivation.

Results The results showed a steady increase in poor SRH over the 10-year duration of the study. A quadratic (inverted U-shaped) trend was observed in material deprivation in the standards of living, which rose from 2001 to 2005, and then declined in 2011. A similar but non-significant trend was found in relative and absolute inequalities in SRH by material deprivation, which increased from 2001 to 2005 and then declined.

Conclusions Inequality in SRH by material deprivation was relatively stable; however, an observed quadratic trend coincided with active and passive labour market reforms in Germany in early 2005.

  • DEPRIVATION
  • SELF-RATED HEALTH
  • SOCIO-ECONOMIC

https://doi.org/10.1136/jech-2015-205948

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    Introduction

    Socioeconomic inequalities in health are a major focus of epidemiological research and health policy. Research on the magnitude of health inequalities and trends in these inequalities has produced mixed findings due, in part, to lack of conceptual clarity and a standardised approach to measure socioeconomic status.1 ,2 Several concepts of measuring material deprivation have been introduced focusing on adolescents3 and adults,4 and area-level deprivation in regions, cities or neighbourhoods.5 The standard of living is a valuable new approach to understanding how socioeconomic deprivation relates to health on the individual level.6 ,7 The approach assumes that in a market economy, the living standard depends on financial resources, such as income and other financial assets, that are provided by private and public sources. Education and occupation contribute indirectly to the living standard by determining financial capabilities.2 ,8 According to Townsend,9 the living standard approach includes absolute or minimum needs, such as adequate food, housing and clothing, as well as relative commodities and activities that are needed to adequately participate in society (ie, a consensual approach). For example, mobile phones, computers and the access to the internet were not available 30 years ago but are now considered necessities for everyone in developed countries such as the UK.10 Inequality in owning such commodities due to lack of financial means, therefore, implies social exclusion and relative or material deprivation.11 ,12

    Research on the association between material standard of living and health may help to better understand the mechanisms that underlie socioeconomic inequalities in health, and guide social and public health policy approaches to reduce these inequalities. Recent research found that the standard of living is a robust social determinant of individual health.6 ,13–19 For example, Pfoertner et al17 found in data from the German Socio-Economic Panel (GSOEP) that differences in material standard of living resulted in larger inequalities in self-rated health (SRH) than differences in income, education or occupational status. Other studies found similar results and suggest that the lack of a minimum level of living standard involves long periods of financial shortages.14 ,16 For example, Whelan et al20 found in 10 European countries a positive association between material deprivation and the duration of income poverty. Therefore, the standard of living may have a larger impact on health than other indicators of socioeconomic status.17 Furthermore, the living standard approach more often measures goods and activities of forced savings (eg, not replacing worn out furniture, saving money for emergencies) and constraints on socially perceived needs (eg, eating a hot meal with meat, inviting friends for dinner), which contribute to individual health via material, psychosocial and behavioural pathways.16

    The extant research on the association between individual standard of living and health has not focused on time trends. Understanding trends in health inequalities by material deprivation is vital to better understand its underlying mechanisms and to evaluate the impact of health and welfare policies on these health inequalities.21 Thus, while the major aim of this study was to assess trends in health inequalities by material deprivation, we also attempted to interpret these trends based on changes in active and passive labour market policies in Germany from 2001 and 2011. Germany is ideal for this study because it experienced major changes in labour market policies in the 1990s and 2000s, which transformed the German economy from a conservative to a liberal labour market.22 A recent literature review of 41 studies concluded that socioeconomic inequalities in health have increased in Germany and other European countries.23 Since the late 1990s, Germany experienced a rise in income inequality and income-related health inequalities.24–28 Given these findings, we hypothesised that relative and absolute health inequalities by material deprivation have increased from 2001 to 2011. However, we also hypothesised that the rise of health inequalities was rather flat as some items of individual living standard are more likely to be affected by long-term shortages (eg, housing problems).29

    Methods

    We analysed longitudinal data from the GSOEP Study (V.29). The GSOEP is a representative annual survey of individuals living in private households in Germany issued by the German Institute for Economic Research (DIW) since 1984.30 Its aim is to evaluate change and stability in living conditions in Germany through face-to-face interviews (about 50%) or self-administered surveys conducted either by paper-and-pencil questionnaires (about 35%) or by mail (about 15%). Since 1984, samples were added to the GSOEP to account for panel attrition and demographic changes that took place in Germany. The current version consists of 10 subsamples of West Germans (1984), foreigners (1984), East Germans (1990), immigrants (1994/1995), three refreshment samples (1998, 2006, 2009), an innovation sample (2000, 2009) and a high-income sample (2002). All samples in the GSOEP are multistage random samples of regional clusters, and households are most often identified by random walk. As outlined by Kroh,31 the recontact rate of households between two survey cycles in the GSOEP was very high, with more than 99% in almost all subsamples. Similarly, the annual reinterview rate exceeded 80% in all subsamples. The GSOEP provides cross-sectional sample weights which have been shown to produce a nationally representative sample.30

    Our analyses were based on five consecutive panel waves between 2001 and 2011 as the GSOEP evaluates the current living standard only every 2 years (with the exception of 2009). We used imputed income data due to high levels of missing values (ranging from 5.5% to 6.1%) compared with the other variables (<1%). The imputed data on income were based on multivariate imputation by chained equations (MICE) carried out by the GSOEP. The MICE procedure replaces all missing values with randomly selected observed values. Missing income values were imputed sequentially 10 times, and for East and West Germany, separately. The imputation model contained information on the household composition, the financial situation of the household, the partial non-response rate, and cross-sectional weights.32 We excluded respondents with missing information. Sample sizes differed only slightly by panel wave (table 1).

    View this table:
    Table 1

    Sample characteristics by survey year (German Socio-Economic Panel)

    Measures

    Self-rated health

    SRH was measured by asking individuals to assess their general health with the question: “In general, how would you describe your current health status?”. From this item, we created a dichotomous outcome measure (very good/good/satisfactory vs poor/bad).33 SRH has been widely used as an indicator of subjective health in public health research; it has shown to be a reliable and valid indicator of general health and mortality, and is recommended by the WHO for health monitoring.33–37

    Material deprivation and the material standard of living

    Material deprivation was measured using 11 items in the household questionnaire of the GSOEP that described the material standard of living. Individuals were asked whether they had (1) a colour television, (2) a telephone or (3) a car, and whether (4) they could replace furniture which is worn out with new furniture, (5) their flat is located in a building which is in good condition, (6) their building is located in a good neighbourhood, (7) they could pay the rent or the payment or mortgage/interest payments on time, (8) they have put some money aside for emergencies, (9) they take a vacation away from home for at least 1 week every year, (10) they invited friends over for dinner at least once a month, and (11) they eat a hot meal with meat, fish or poultry at least every other day. Negative responses to these living standard items were followed up with a question that asked if these were lacking due to financial or other reasons. The indicators reflect a short list of the basic and extended necessities in Germany according to previous social surveys.41 ,42 In the GSOEP, the internal consistency of the 11 living standard items was stable across survey cycles and relatively moderate (Cronbach's α ranged from 0.54 to 0.63). We constructed an unweighted additive index, ranging from 0 to 11, to indicate the number of standard of living items missing due to financial reasons. To examine inequalities in health between the highest and the lowest socioeconomic groups, this index was transformed to cumulative rank probabilities ranging from 0 (the lowest material deprivation) to 1 (the highest material deprivation).43

    Control variables

    The analyses controlled individual differences in factors that were known to relate to SRH and socioeconomic disadvantage: age, gender, marital status (married, in a relationship, single), and residence (East or West Germany), occupational status, education, and income class (table 1).

    Statistical analyses

    The statistical analyses begin with a descriptive presentation of trends in mean levels of poor SRH and material deprivation. Mean values with 95% CIs based on cross-sectional weights are presented in figure 1. To identify the significance of linear or curvilinear trends of poor SRH and material deprivation, we fitted a crude linear regression model with a trend variable (linear and quadratic variable depending on the observed time trend).

    Figure 1
    Figure 1

    Mean of poor self-rated health and material deprivation between 2001 and 2011, with 95% CIs (weighted data, German Socio-Economic Panel 2001–2011).

    Inequalities in SRH due to material deprivation were calculated using the relative index of inequality (RII) and the slope index of inequality (SII).44 ,45 The RII and SII are measures of relative and absolute inequalities in health, respectively, and have been widely used in cross-comparative epidemiological research.43 These indices summarise health inequality between the highest and the lowest socioeconomic groups, in either absolute or relative terms. Two-sided 95% CIs for the RII and SII were estimated based on pooled interval logistic regression models and calculated as relative risk differences (RII) and absolute risk ratios (SII) between the highest and the lowest material living standard, using the adjustment method proposed by Norton et al.46

    Pooled interval logistic regression models were estimated with robust SEs taking into account the clustering of observations across time within a respondent.47 ,48 Stepwise regression was used to examine factors affecting relative and absolute inequalities in SRH by material deprivation. First, a univariate model including material deprivation measure was fitted to the data (Model 1, M1). M2 was based on M1, and also included sociodemographic characteristics. M3a–3c were based on M2 and also adjusted separately for education, occupational status and income to identify their single impact on inequalities in SRH. M4 was the full model and examined trends in relative and absolute inequalities in SRH by material deprivation after adjusting for all covariates. All model specifications tested linear and quadratic time trends in inequalities in SRH. The degree of model fit was assessed with McFadden's pseudo R2.49 McFadden's R2 ranges from 0 to 1, with higher values indicating a better model fit. Values between 0.2 and 0.4 are considered to be indicative of excellent model fit. Correlations were conducted to evaluate the collinearity of material deprivation with income and education (Pearson's product moment correlation) and occupational status (point biserial correlation). Analyses were performed with Stata 13.0 (StataCorp, Texas, USA).

    Results

    Trends in rates of poor SRH and average material deprivation were shown in table 1 and figure 1. Poor SRH increased steadily from 16.1% to 18.8%, with a significant linear trend over the 10-year duration of the study (linear trend variable in regression: p<0.001). The linear trend in poor SRH was not significant after age differences were controlled (p=0.153). Mean levels in material deprivation significantly rose from 2001 (0.79) to 2007 (1.01) (linear trend variable in regression: p<0.001), and then declined significantly to 0.90 in 2011 (quadratic trend variable in regression: p<0.001). The results were unaltered if models were adjusted for age (results not shown).

    Tables 2 and 3 present the results of the multivariate analysis of trends in relative and absolute health inequalities. In all model specifications, the relative risks and mean levels of poor SRH were significantly higher in the most deprived compared with the least deprived group in terms of material living standards. Except for M1 in tables 2 and 3, a slight (non-significant) curvilinear trend was observed with an increase in inequalities up to a certain point in time, followed by a decline. In the full model (M4), inequalities in SRH by material deprivation increased between 2001 and 2005, and declined in 2011 (figure 2). Relative inequalities in SRH between the highest and the lowest living standards rose from 2.22 to 2.34 between 2001 and 2005, and decreased to 2.27 in 2011 (table 2). Absolute inequalities in mean levels of poor SRH by material deprivation also rose from 0.13 to 0.15 between 2001 and 2005, and decreased to 0.14 in 2011 (table 3). However, trend coefficients were not significant indicating that relative and absolute inequalities in SRH by material deprivation were remarkably stable over time. The final M4 showed a moderate fit to the data and offered the best fit compared with any simpler model (McFadden's pseudo R2=0.103).

    View this table:
    Table 2

    Relative inequalities in poor self-rated health by material deprivation (RII) between 2001 and 2011 (German Socio-Economic Panel 2001–2011)

    View this table:
    Table 3

    Absolute inequalities in poor self-rated health by material deprivation (SII) between 2001 and 2011 (German Socio-Economic Panel 2001–2011)

    Figure 2
    Figure 2

    Relative and absolute inequalities in poor self-rated health between 2001 and 2011, with 95% CIs (German Socio-Economic Panel 2001–2011) (RII, relative index of inequality; SII, slope index of inequality).

    The trend and extent of inequalities in SRH by material deprivation were influenced by sociodemographic and socioeconomic factors (tables 2 and 3). In comparison to M2, in M1 the effects of material deprivation were underestimated as age was omitted, which was negatively related to SRH (poorer health in older age groups) and negatively related to material deprivation (higher among younger age groups; for age-stratified analyses see online supplementary table S1). Age-stratified analyses showed that relative inequalities in SRH by material deprivation were highest in the middle-age groups, whereas absolute inequalities in SRH by material deprivation were highest in the oldest age group (aged 65+). The oldest age cohort showed the only significant trend in SRH by material deprivation with an inverted U-shaped pattern.

    In M3a, M3b and M3c, inequalities in SRH by material deprivation were found to decrease due to the interaction of socioeconomic factors with SRH and material deprivation. We observed the largest decrease in relative risks and absolute differences in poor SRH after adjusting for income (M3c). Accordingly, strongest correlation of material deprivation with the socioeconomic factors was observed for income (r=−0.44) compared with education (r=−0.16) and occupational status (point biserial correlation for low=0.10, moderate=−0.04 and high occupational status=−0.10, and for vocational training=0.03, unemployment=0.24, economically inactive=−0.08 and others=0.00).

    All observed patterns over time were similar for relative (RII) and absolute (SII) inequalities in SRH by material deprivation. None of the observed trends were statistically significant, thus indicating a stable relationship between material deprivation and SRH over time. Focusing on the absolute differences in mean levels of poor SRH indicated a very low change over time, which might be overestimated by relative inequalities in SRH.

    Discussion

    This study examined trends in relative and absolute inequalities in SRH between the highest and the lowest levels of material deprivation in a representative cohort of German adults. The assessment of deprivation adopted a material standards of living approach, and thus accounted for basic and extended necessities in Germany and changes in these standards from 2001 to 2011. Moreover, we also tested whether the trend of inequalities in SRH by material deprivation were influenced by income, education and occupation.

    The results showed a steady increase in poor SRH over the 10-year duration of the study. A quadratic (inverted U-shaped) trend was observed for material deprivation on standards of living, which rose from 2001 to 2005 and then declined. Similar trends were found in relative and absolute inequalities in SRH by material deprivation, which increased from 2001 to 2005 and then declined. The increase in inequalities in SRH by material deprivation was not significant, but corresponds to the introduction of the strongest labour market reforms in Germany in early 2005.25 Improvements in health during the first half of the decade disproportionately favoured the least deprived groups. The second half of the decade, following the market reforms of 2005, was a period of health equalisation between socioeconomic groups.

    Other studies found that perceived shortcomings in social participation and prestige, and constraints of material deprivation on welfare recipients of ‘unemployment benefit II’ (Arbeitslosengeld II) have increased during the new labour market reforms.42 ,50 This benefit scheme was introduced in early 2005 as a means-tested and tax-funded basic security scheme for job seekers and replaced the former social assistant benefits in Germany (Sozialhilfe).22 ,51 Siegel et al25 also found increased health inequalities during the Hartz reforms in early 2005, which coincided with increased unemployment, underemployment, and in-work poverty and reduced unemployment benefits.

    Our results contradict previous findings that showed a steady increase in socioeconomic inequalities in SRH in German adults by income or occupation in the past two decades.23 ,25 ,28 ,52–54 Stable trends in inequalities in SRH by income and education were also found in a German city (Augsburg) between 1984 and 2000.55 Only one study by Kroll and Lampert56 found a similar inverted U-shaped trend in the association of income with SRH between 1994 and 2008 in the GSOEP. It is possible that the introduction of labour market reforms had only a short-term influence on inequalities in SRH by material deprivation as observed in trends of unemployment in Germany, which also rose in 2005 and then declined.57 However, because the effects of material deprivation were not strongly influenced by occupational status, we are cautious not to exaggerate the contributions of unemployment on this trend. Furthermore, the short-term increase in health inequality might also reflect a process of social adjustment to labour market reforms as the specific changes in the regulations were not fully transparent.58

    This study also found that income related more closely to the association between material deprivation and SRH than education and occupational class. However, trends in inequalities in SRH by material deprivation did not correspond with previous studies that found a steady increase in income inequality and income-related inequalities in health in Germany.24–28 Unlike income, the standard of living measures periods of persistent income poverty and socioeconomic deprivation.59–61 A certain standard of living requires longer periods of financial investments, while the loss of standard of living requires longer periods of financial shortages.17 ,59 ,61 ,62 In addition, several factors, such as property ownership, age, education, employment and marital status, further contribute to individual's living standard.59 ,61 In our study, age strongly influenced inequalities in SRH as the mean level of poor SRH was higher among older age groups, whereas material deprivation was higher among younger age groups.

    Strengths and limitations

    Strengths of the study include its large representative sample of adults, consistency in sampling and measurement over five successive panel waves, and multiple indicators of socioeconomic status. Also, the use of the RII and SII provided a more complete account of trends in inequalities in SRH than that either could index alone. Relative and absolute inequalities in health can show different trends over time due to changes in population health or disease prevalence.63 ,64 Additionally, the study demonstrated the value of multiple socioeconomic indicators in isolating the impact of material deprivation on health. It was important to control for confounding effects of education, income and occupational status on material deprivation and on SRH.

    Our study also has limitations. Ideally, a thorough evaluation of the impact of material deprivation requires information about the physical and psychosocial health status, and these data were unavailable in the GSOEP. Furthermore, a consistent trend analysis could not be established in the GSOEP due to the fragmentary structure of its longitudinal data set. Analysis on the long-term effects of labour market reforms on material deprivation and inequalities in health ideally involves longer periods of follow-up. Therefore, it would be useful to extend the time frame of this study using additional panel waves. Also, a central challenge in the measurement of standard of living is the adequate measurement of perceived necessities of the population and its subgroups. For example, it has been shown that individuals adapt their preferences towards a specific living standard to what is economically achievable.41 Moreover, their perceptions of the necessities of an acceptable standard of living might change in time and thereby, influence the effect of material deprivation on health. However, the attitudes towards most items did not change substantially according to a comparison of data in 1996, 1998 and 2006/2007, and the effects of material deprivation were stable over time.41 ,42 Moreover, the evaluation of individuals’ living standards could not reflect differences in the quality, quantity, and distribution of current living standard items within a household. The internal consistency of the living standard scale was moderate indicating that the index consists of different dimensions of material deprivation, which Fusco et al65 described as economic strain, enforced lack of durables, and housing. Therefore, the association between material deprivation and SRH might differ between dimensions of material deprivation. Further studies should take this into account. Finally, comparisons with other studies were limited because evidence about trends in inequalities in SRH among German adults is scarce.23 Existing trend studies for Germany are heterogeneous as they have focused on different time periods, health outcomes and populations.

    Conclusion

    This 10-year longitudinal study of German adults found complex trends in average SRH and inequalities in SRH as defined by material standards of living. We observed a linear trend of increasing poor SRH with a U-shaped trend in material deprivation of standards of living. A converse but not significant trend in relative and absolute inequality in SRH by material deprivation (ie, growing inequality from 2001 to 2005 to equalisation in SRH from 2005 to 2011) coincided with market reforms of early 2005 in Germany. An increase in income inequality during the decade did not coincide with a similar increase in inequality in SRH by material deprivation in standards of living.

    What is already known on this subject

    • International studies showed a strong association between socioeconomic status and health and health behaviours.

    • Measures of socioeconomic status were differently associated with health and trends in health.

    • The material standard of living has been neglected in health research as an outcome of socioeconomic status and as a determinant of health.

    What this study adds

    • Our study provides first evidence on trends of relative and absolute inequalities in self-rated health (SRH) as defined by material deprivation in Germany.

    • The standard of living is a valuable new approach that focuses on the material outcome of individuals’ socioeconomic status as a determinant of health.

    • Material deprivation was significantly associated with SRH independent from income, education and occupational status.

    • Although inequalities in SRH by material deprivation were relatively stable between 2001 and 2011, the observed U-shaped trend seemed to coincide with active and passive labour market reforms in Germany in early 2005.

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    Supplementary materials

    • Supplementary Data

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    Footnotes

    • Contributors T-KP initiated the idea, designed and wrote the first draft of the manuscript, and analysed the data. FJE was involved in the analysis and interpretation of data, and critically reviewed the manuscript.

    • Competing interests None declared.

    • Provenance and peer review Not commissioned; externally peer reviewed.

    • Data sharing statement This study used anonymised secondary data of scientific use files, which could be viewed at http://www.diw.de/en/soep.