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Josie Machalek

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Josie Machalek

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Jack Stiele

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Journal of Epidemiology & Community Health

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Abstract

Background: The infant mortality rate (IMR) has been criticised as a measure of population health because it is narrowly based and likely to focus the attention of health policy on a small part of the population to the exclusion of the rest. More comprehensive measures such as disability adjusted life expectancy (DALE) have come into favour as alternatives. These more comprehensive measures of population health, however, are more complex, and for resource poor countries, this added burden could mean diverting funds from much needed programmes. Unfortunately, the conjecture, that DALE is a better measure of population health than IMR, has not been empirically tested.

Methods: IMR and DALE data for 1997 were obtained from the World Bank and the World Health Organisation, respectively, for 180 countries.

Findings: There is a strong (generally) linear association between DALE and IMR ( r=0.91). Countries with low DALE tend to have a high IMR. The countries with the lowest IMRs had DALEs above that predicted by the regression line.

Interpretation: There is little evidence that the use of IMR as a measure of population health has a negative impact on older groups in the population. IMR remains an important indicator of health for whole populations, reflecting the intuition that structural factors affecting the health of entire populations have an impact on the mortality rate of infants. For countries with limited resources that require an easily calculated, pithy measure of population health, IMR may remain a suitable choice.

METHODS

The relation between IMR and DALE was examined in all 180 countries for which data were available.

The DALE data for 1997/1999 for the total population at birth in each country were obtained from The World Health Report 2000 (annex table 5). The IMR data for 1997 were obtained from the World Bank's Development Indicators.

RESULTS

The distribution of IMRs for the 180 countries was skewed with a long right tail. The median IMR was 29 (Vietnam) and the interquartile range lay between 12 (Costa Rica) and 70 (Senegal) (see fig 1). The country with the lowest IMR was Japan (3.7) and Sierra Leone had the highest IMR (170).

Similarly, the distribution of DALEs was skewed, although, in this case the distribution had a long left tail. The median DALE was 60.5 (Grenada) and the interquartile range lay between 46.9 (Papua New Guinea) and 65.7 (Antigua) (see fig 1). The country with the highest DALE was Japan (74.5) and the country with the lowest was Sierra Leone (25.9).

Figure 2 shows a scatter plot with the regression line of the relation between IMR and DALE.

There are a number of striking features about the plot. Firstly, there is a strong (generally) linear relation between IMR and DALE ( r=0.91). As IMRs rise, DALEs fall. Secondly, there are a group of countries with very low IMRs for which the linear relation no longer seems to hold. Indeed, as the DALE rises beyond about 69 years the IMR seems to asymptote, suggesting a lower limit to the IMR around Japan's rate of 3.7. Finally, the countries with low IMRs and high DALEs tend to fall tightly around the regression line, whereas the countries with high IMRs and low DALEs are more dispersed around the line (an example of heteroscedasticity). The standard deviation of the DALE for those countries with an IMR less than the median (29) was 4.5 while for those with an IMR greater than the median it was 10.6. A similar pattern was observable in the variability of the IMR data. The countries with an IMR greater than 29 showed the greatest variability in DALE, and they were without exception developing countries.

Each of these observations has significant implications for health planners choosing a measure of population health.

DISCUSSION

The strong linear relation between IMR and DALE means that IMR accounts for more than 80% of the variance of the DALE. It suggests that, in general, one measure could stand as a proxy for the other, and either could stand as a proxy for the measurement of population health. Indeed, there is little evidence that IMR is any worse than the DALE as a measure of population health.

The fact that there is greater dispersion around the regression line for the developing countries with IMRs greater than 29 suggests measurement error. The poorest countries with the least developed infrastructure are least able to collect accurate data for the calculation of the IMR or DALE. Furthermore, given that the calculation of the DALE requires the collection of more data than is required for the calculation of IMR, one might speculate that the DALE has more opportunity for measurement error to creep in and is, therefore, likely to be a less reliable measure.

If health policy were, as conjectured, going to be unduly influenced by IMR, then one would expect to have observed the effects most in those countries with the lowest IMRs. It is after all those countries with the lowest IMRs that are most likely to have concentrated their efforts on lowering infant mortality to the exclusion of the rest of the population. This should result in an uncharacteristically low DALE inconsistent with the regression line. The presence of the "asymptotic countries" with very low IMRs that sit above the regression line suggests that quite the contrary has occurred and governments have not had their health policies shackled by the use of IMR as an indicator of population health. Between these asymptotic countries however, there is little variation in either their DALE or their IMR, and this suggests that, for them, more sensitive measures of population health may be required.

The fact that the IMR and the DALE are so highly correlated merely goes to reinforce the intuition that the causes of infant mortality are strongly related to those structural factors like economic development, general living conditions, social well being, and the quality of the environment, that affect the health of entire populations. This also goes some way to answer why it is that a measure of pure mortality in infants could be so highly correlated with a measure of mixed mortality and morbidity over an entire population that includes dimensions of disability and severity.

Furthermore, because IMR is sensitive to structural changes as well as disease epidemics, it becomes an important indicator of "here and now" effects. Rapid changes in the determinants of population health captured by changes in IMR may be slow to be reflected in DALE, which is influenced by factors such as long term survival and morbidity-mirrored in features like birth cohort effects.

CONCLUSION

The IMR remains a useful and comparatively inexpensive indicator of population health. Its explanatory power is very similar to that of the DALE.

That is not to say that the collection of additional epidemiological data about the health of a population would not be advantageous. Multiple measures, particularly measures that can be disaggregated by age, gender, health condition, socioeconomic status, etc, will always be important for planning. However, if resources are limited, and a pithy, uncomplicated measure of population health is required, then countries with IMRs greater than 10 would seem to be safe using IMR as the indicator.

Acknowledgments

We would like to thank the two anonymous reviewers for contributing their ideas to the final form of this paper.

View Abstract

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Infant mortality rate as an indicator of population health

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Background: The infant mortality rate (IMR) has been criticised as a measure of population health because it is narrowly based and likely to focus the attention of health policy on a small part of the population to the exclusion of the rest. More comprehensive measures such as disability adjusted life expectancy (DALE) have come into favour as alternatives.

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Jack Stiele

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International Journal for Equity in Health

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Measuring health inequality among children in developing countries: does the choice of the indicator of economic status matter?

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Currently, poor-rich inequalities in health in developing countries receive a lot of attention from both researchers and policy makers. Since measuring economic status in developing countries is often problematic, different indicators of wealth are used in different studies.

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Jack Stiele

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The health of people living in developing countries around the world has improved considerably over the past 2 decades. For example, the total number of deaths annually among children less than 5 years of age has been halved over the past 40 years. Unfortunately, in most of sub-Saharan Africa and some parts of South Asia, these reductions in mortality have stagnated or even reversed over the past decade. At the same time, disease patterns and causes of death in less developed countries have changed markedly. The most obvious example of such change relates to HIV/AIDS, but others include the re-emergence of tuberculosis as a global health problem, the emergence of new infectious diseases, the increase in violence and the occurrence of chronic diseases formerly thought to be of concern only in developed countries, such as coronary artery disease and cerebrovascular accidents. Global monitoring of changes in the health of various populations requires the use of "tried and true" global health indicators. However, we also need indicators that are relevant to contemporary patterns of disease and their determinants.

This overview and the accompanying glossary of global health indicators (see the online appendix at www.cmaj.ca/cgi/content/full/171/10/1199/DC1) are intended to assist readers in understanding and interpreting summaries of global health statistics reported in professional journals and multinational publications, such as UNICEF's annual report, The State of the World's Children (see text ). Several global health indicators, such as infant mortality rate, are well known to health professionals working in both developed and developing countries. However, many others are not well understood and tend to bewilder readers or create "statistical overload" rather than accomplishing the intended purpose of improving understanding.

Global health indicators can be divided into those that directly measure health phenomena (e.g., diseases, deaths, use of services) and indirect measures (e.g., social development, education and poverty indicators); these are also referred to as proximal and distal indicators respectively. On the basis of population statistics describing levels of education attained and access to safe water and sanitation, it is possible to categorize a country fairly accurately as having a population with high, medium or low burden of disease. It is beyond the scope of this overview to address all potential indicators, and the glossary therefore focuses on direct measures of health, population and nutrition (or services related to these areas). The global health indicators used in developing countries for the most part address morbidity, mortality and important precursors of both. In contrast, in developed countries a large proportion of the key health indicators reflect lifestyles and individual behaviour, such as physical exercise, smoking, diet, or substance and alcohol abuse.

Because of cost constraints and limited logistic capacity, few developing countries are able to maintain death, birth or disease registries. Data generated by health care institutions are more readily available and more frequently used, but must be viewed with caution because they are not representative of the general population. In developing countries, a biased minority of the population (typically urban, wealthy and better educated) use modern medical services. Furthermore, for several presenting health problems, only patients exhibiting the most severe end of the spectrum ever reach a health care facility. Fortunately, alternative, technologically appropriate, affordable data collection methods have been adopted in many developing countries, including national demographic and health surveys, one-off ecologic or household surveys, multiple-indicator cluster surveys, verbal autopsies and demographic surveillance systems within selected populations. A combination of data from these sources is then used to assess the health status of the nation as a whole or regionally.

There are far more health indicators to choose from than any health information system can reasonably include. In developing countries, because of severely restricted resources and capacities, there is a need to select a limited set of indicators that are clearly applicable to monitoring, decision-making and health policy, and to measure them well. What characteristics should guide the selection of a global health indicator? Few indicators meet all of the following criteria, but some do much better than others.

Definition. The indicator must be well defined, and the definition must be uniformly applied internationally.

Validity. The indicator must be valid (it must actually measure what it is supposed to measure), reliable (replicable and consistent between settings) and readily interpretable.

Feasibility. The gathering of the required information must be technologically feasible and affordable and must not overburden the system.

Utility. The indicator should provide information that is useful to decision-makers and can be acted upon at various levels (local, national and international).

The validity of published health statistics from developing countries is variable and extremely difficult to assess. Validity can be threatened in several ways. For instance, it is adversely affected by variations between countries in definitions of health and illness states, by the choice of easy-to-reach but usually unrepresentative populations for surveys, and by the underestimation or overestimation of denominators. Denominators tend to be based on the most recent census and the application of crude death and birth estimates. However, such data are often out of date and are vulnerable to manipulation. Numerators, such as the occurrence of an illness or health behaviour, are also subject to multiple sources of error. They depend on a respondent's capacity to understand the question and to recall an event or exposure, as well as a willingness to report what he or she recalls.

How can the validity and utility of global health indicators be improved? Countries and health care systems with restricted resources can consider several options, including the following:

measurement of a smaller number of indicators, specifically those with direct relevance to decision-making and high-priority health issues

use of more efficient sampling frames and procedures

continued refinement and validation of verbal autopsies

application of standard, internationally accepted definitions.

Despite the acknowledged limitations of many health indicators and the reservations one might have about the accuracy of health statistics derived in developing countries, they nonetheless do provide useful estimates of a population's state of health. Although the absolute estimates may lack accuracy, they constitute a valuable "yardstick" by which to monitor change within a population over time. Comparison between countries is also possible, but is more susceptible to information and selection bias. Global health indicators highlight the tremendous disparities in health status within a given population or between developing and developed countries. Within-country and subpopulation comparisons are becoming more common as health care professionals in the developing world become more aware of and more concerned about the performance of health care systems and issues of equity in relation to gender, socioeconomic status, ethnicity and geography.

In summary, it is reasonable to question the accuracy of global health indicators reported from developing countries. However, intermediate technologies applied by developing countries, such as national demographic and health surveys, do produce acceptable estimates of these indicators and can provide valuable information for policy-makers, allowing them to monitor equitable progress toward healthier populations.

β See related article page 1203

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Josie Machalek