Trends in socioeconomic health inequalities in the Netherlands, 1981-1999. .

Study objective: To determine changes in socioeconomic inequalities in self reported health in both the 1980s and the 1990s in the Netherlands.

Design: Analysis of trends in socioeconomic health inequalities during the last decades of the 20th century were mode using data from the Health Interview Survey (Nethhis) and the subsequent Permanent Survey on Living Conditions (POLS) from Statistics Netherlands. Socioeconomic inequalities in self assessed health, short-term disabilities during the past 14 days, long term health problems and chronic diseases were studied in relation to both educational level and household income. Trends from 1981 to 1999 were studied using summary indices for both the relative and absolute size of socioeconomic inequalities in health.

Setting: The Netherlands.

Participants: For the period 1981-1999 per year a random sample of about 7000 respondents of 18 years and older from the non-institutionalised population.

Main results: Socioeconomic inequalities in self assessed health showed a fairly consistent increase over time. Socioeconomic inequalities in the other health indicators were more or less stable over time. In no case did socioeconomic inequalities in health seemed to have decreased over time. Socioeconomic inequalities in self assessed health increased both in the 1980s and the 1990s. This increase was more pronounced for income (as compared with education) and for women (as compared with men).

Conclusion: There are several possible explanations for the fact that, in addition to stable health inequalities in general, income related inequalities in some health indicators increased in the Netherlands, especially in the early 1990s. Most influential were perhaps selection effects, related to changing labour market policies in the Netherlands. The fact that the health inequalities did not decrease over recent years underscores the necessity of policies that explicitly aim to tackle these inequalities.

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It has often been shown that people of lower socioeconomic groups more often suffer from ill health. Much less is known about the changes over time in health inequalities between socioeconomic groups. For various reasons, it is important to study these changes. Firstly, for setting priorities in the field of public health it is important to know whether health inequalities are widening or decreasing. Secondly, it is important to know whether socioeconomic inequalities in health change to evaluate policies aimed at reducing these differences. Thirdly, studying the changes in socioeconomic health inequalities is a way to better understand the background of these inequalities, for example, to determine the sensitivity of health inequalities to changes in the relative income of different socioeconomic groups. Finally, analyses of past trends are necessary for making predictions of future trends in inequalities in health.

Most studies on trends in socioeconomic health inequalities have analysed mortality data. There has been comparatively little research on trends in socioeconomic inequalities in morbidity indicators like self reported health. Most studies on trends in inequalities in self reported health looked at self assessed health. (1-9) There are only a few studies on trends in health inequalities in self reported health that look at other health indicators like limiting longstanding illness, (4-6, 10) chronic diseases, (8,11) and short-term limitation during the past 14 days. (8,9,11)

The literature on trends in socioeconomic inequalities in self assessed health has produced inconsistent results. For example, the results concerning self assessed health are contrasting. Inequalities in self assessed health between socioeconomic groups have narrowed or remained about stable according to most studies. (1,3-6,8) However, according to other studies these inequalities tended to widen. (2,5) One study first showed a widening and then a narrowing of socioeconomic differences in self assessed health. (7) These trends could also differ somewhat between men and women. A few studies indicated that socioeconomic health inequalities remained about the same for women while they narrowed for men. (1,3,4,6)

The evidence on trends in socioeconomic inequalities in self assessed health is not only inconsistent but also fragmentary. Firstly, most studies only used one of the core socioeconomic indicators (education, occupational class, and income). (2-4,6,7) Secondly, the timespan of studies on trends in socioeconomic inequalities in self assessed health varied considerably: some have used data from only a few years out of a longer time span. (2,4-6) There are also studies that cover a period of 10 years (7) or even between 15 and 20 years. (1,3) Thirdly, different upper and lower age limits were used in studies on trends in inequalities in self assessed health. (1,3,5,6) It should finally be noted that most of the internationally published studies come from Finland and a few other countries such as Sweden and Britain. (1,3-7) For the Netherlands, for example, only a few studies are published on trends in socioeconomic health inequalities in self assessed health. (2,9) It is however interesting to study these trends for the Netherlands as it has been a fairly stable country. There was no strong economic recession like in Finland and Sweden in the early 1990s or a strong increase in income inequalities like in Britain. (4,5,12)

In summary, studies on trends in inequalities in self assessed health show contrasting results. In addition, the literature is still highly fragmentary. This study aimed to fill part of the many gaps. We used data from an ongoing national health survey: the Health Interview Survey (NethHIS), (13, 14) which allowed us to construct a comprehensive overview on trends in socioeconomic inequalities in self reported health in the Netherlands. Firstly, we used both education and income as socioeconomic indicators. Secondly, four indicators of self reported health were used: self assessed health, short-term limitations during the past 14 days, long term health problems, and chronic diseases. Finally, we covered a period of 19 years ranging from 1981 until 1999. Altogether this made it possible to compare the results between different health and socioeconomic indicators, and to compare the trends in health inequalities in self reported health during the 1980s to more recent trends during the 1990s.

The following research questions are investigated in this paper. (1) Is there a decrease or increase in the size of socioeconomic health inequalities in self reported health between 1981-1999 in the Netherlands? (2) Is the trend during the 1990s the same as during the 1980s? (3) Are the observed trends consistent for both education and income, for both men and women and for all the above mentioned four health indicators?

METHODS

Data source

The data were derived from an ongoing national health survey: the Health Interview Survey (NethHIS). This survey is carried out by Statistics Netherlands (NCBS). (13,14) This survey started in 1981 and is conducted each year among a random sample of nearly 10 000 respondents from the non-institutionalised population in the Netherlands. This resulted in a representative sample of the non-institutionalised Dutch population. The information from this survey is mainly gathered during face to face interviews. These surveys were held throughout the whole year and took place at the homes of the respondents. The surveys were held in Dutch among persons registered at the municipal population registries. The health survey contains questions on a number of health indicators and socioeconomic indicators.

The Health Interview Survey changed into the Permanent Research on Living Conditions (POLS) in l997. (15) The important changes are that, since the introduction of the POLS, what used to be different surveys in the Netherlands were integrated into one system of level of living studies, and that with the introduction of the POLS proxy interviews were no longer held.

The non-response rate was 32% in 1981 and increased to 44% in 1999. In the discussion section, we will answer the question to what extent this problem may have biased the results.

For this study, we analysed data from the NethHIS and the POLS for the years 1981 until 1999 for all respondents aged 18 years and older.

Health indicators

For this study, four commonly used indicators of self reported health were selected. The first indicator was self assessed health. This indicator was measured with a single item question ("How is your health in general?") with answer possibilities on a 5 point scale: very good, good, fair, sometimes good and sometimes bad, bad. For this study two cut off points were used: "less than good" and "less than fair health".

The second indicator was the prevalence of short-term limitations during the …