Development of an international scale of socio-economic position based on household assets

Abstract

BackgroundThe importance of studying associations between socio-economic position and health has often been highlighted. Previous studies have linked the prevalence and severity of lung disease with national wealth and with socio-economic position within some countries but there has been no systematic evaluation of the association between lung function and poverty at the individual level on a global scale. The BOLD study has collected data on lung function for individuals in a wide range of countries, however a barrier to relating this to personal socio-economic position is the need for a suitable measure to compare individuals within and between countries. In this paper we test a method for assessing socio-economic position based on the scalability of a set of durable assets (Mokken scaling), and compare its usefulness across countries of varying gross national income per capita.ResultsTen out of 15 candidate asset questions included in the questionnaire were found to form a Mokken type scale closely associated with GNI per capita (Spearman’s rank rs = 0.91, p = 0.002). The same set of assets conformed to a scale in 7 out of the 8 countries, the remaining country being Saudi Arabia where most respondents owned most of the assets. There was good consistency in the rank ordering of ownership of the assets in the different countries (Cronbach’s alpha = 0.96). Scores on the Mokken scale were highly correlated with scores developed using principal component analysis (rs = 0.977).ConclusionsMokken scaling is a potentially valuable tool for uncovering links between disease and socio-economic position within and between countries. It provides an alternative to currently used methods such as principal component analysis for combining personal asset data to give an indication of individuals’ relative wealth. Relative strengths of the Mokken scale method were considered to be ease of interpretation, adaptability for comparison with other datasets, and reliability of imputation for even quite large proportions of missing values.

The association between chronic airflow obstruction and poverty in 12 sites of the multinational BOLD study

“…We therefore referred to these scores as "wealth scores", as they are broadly indicative of an individual's wealth. We previously showed that the rank ordering of prevalence of ownership of these assets was fairly consistent across a wide range of countries with GNI/capita ranging from $4750 to $53 760 (Cronbach's alpha=0.96), suggesting that this is a useful scale to compare individuals both within and between countries [12].…”

“…# : individual responses have been weighted according to the probability of selection to provide population estimates of means and percentages for each of the study areas; ¶ : individuals selected for possible inclusion in the Burden of Obstructive Lung Disease (BOLD) study using a random sampling process; + : individuals included in the study (i.e. those who agreed to take part in the BOLD study and provided useable data from both the questionnaire and spirometry tests); § : 1 pack-year equals an average of 20 cigarettes per day for 1 year or the equivalent amount of other types of tobacco smoking; ƒ : somebody else in the household smoked during the past 2 weeks; ## : the respondent was employed in a dusty job for at least 1 year; ¶ ¶ : ever diagnosed with tuberculosis; ++ : a close sibling or parent had been diagnosed as having emphysema, chronic bronchitis or COPD by a health professional; § § : hospitalised for breathing problems before the age of 10 years; ƒƒ : highest level of education completed was above primary school; ### : calculated from ownership of a range of assets (see methods and [12]); ¶ ¶ ¶ : exposure to open fires for cooking and/or heating for more than 20 years; +++ : current or ex-smoker. the present analysis, as the questions on household assets were only introduced into the BOLD protocol at a relatively late stage.…”

“…Where the quality of any technician fell below the quality required for the programme, the technician was temporarily withdrawn and re-trained. The current analysis included the 12 sites that entered the study after new questionnaires that included the 15-item asset inventories used to create a measure of individual wealth were introduced [12].…”

“…The scores of individuals were calculated by adding up the total number of these assets owned by the respondent or their household; the scores were therefore in the range 0 (no assets) to 10 (all assets). Previous work showed that the number of assets owned was correlated with educational level and other variables likely to be related to socioeconomic position, and the mean number of assets owned in each country was highly correlated with the GNI per capita of the particular country being surveyed [12]. We therefore referred to these scores as "wealth scores", as they are broadly indicative of an individual's wealth.…”

Poverty cannot be inhaled and it is not a genetic condition. How can it be associated with chronic airflow obstruction?

“…An alternative approach to poverty which is frequently used in health studies is the assessment of socioeconomic status (SES), a composite measure of a person's economic and social position generally based on income, occupation, education level, and home and neighbourhood conditions and environment [9]. Although some authors have questioned the assets-based methods [10], the wealth score used in Townend's study has shown close correlation with the education level and gross national income per capita of the country [11].…”