Assessment of Bias in National Growth-monitoring Data: A Case Study in Zimbabwe

This study assesses the extent to which children under five years of age attending a growth-monitoring program are representative of the population as a whole. Bias in the prevalence of underweight estimated through growth-monitoring is assessed by comparing data from the program with prevalence estimates from the community-based Demographic and Health Surveys of 1988 and 1994. Geographic patterns of attendance at growth-monitoring are also examined through a comparison with census data, and trends in growth-monitoring data are also assessed. Provincial and national estimates of the prevalence of underweight from the two sources were not significantly different in 1988, but significant differences in prevalence estimates were identified in 1994. This suggests that growth-monitoring attendees were less representative of the general population in 1994 than at the start of the study period. The methodology used is transferable elsewhere, since the same data sets exist for many other African countries.

Methods of nutrition surveillance in low-income countries

BACKGROUND

In 1974 a joint FAO/UNICEF/WHO Expert Committee met to develop methods for nutrition surveillance. There has been much interest and activity in this topic since then, however there is a lack of guidance for practitioners and confusion exists around the terminology of nutrition surveillance. In this paper we propose a classification of data collection activities, consider the technical issues for each category, and examine the potential applications and challenges related to information and communication technology.

ANALYSIS

There are three major approaches used to collect primary data for nutrition surveillance: repeated cross-sectional surveys; community-based sentinel monitoring; and the collection of data in schools. There are three major sources of secondary data for surveillance: from feeding centres, health facilities, and community-based data collection, including mass screening for malnutrition in children. Surveillance systems involving repeated surveys are suitable for monitoring and comparing national trends and for planning and policy development. To plan at a local level, surveys at district level or in programme implementation areas are ideal, but given the usually high cost of primary data collection, data obtained from health systems are more appropriate provided they are interpreted with caution and with contextual information. For early warning, data from health systems and sentinel site assessments may be valuable, if consistent in their methods of collection and any systematic bias is deemed to be steady. For evaluation purposes, surveillance systems can only give plausible evidence of whether a programme is effective. However the implementation of programmes can be monitored as long as data are collected on process indicators such as access to, and use of, services. Surveillance systems also have an important role to provide information that can be used for advocacy and for promoting accountability for actions or lack of actions, including service delivery.

CONCLUSION

This paper identifies issues that affect the collection of nutrition surveillance data, and proposes definitions of terms to differentiate between diverse sources of data of variable accuracy and validity. Increased interest in nutrition globally has resulted in high level commitments to reduce and prevent undernutrition. This review helps to address the need for accurate and regular data to convert these commitments into practice.

Measuring Anthropometric Indicators through Nutrition Surveillance in Humanitarian Settings: Options, Issues, and Ways Forward

The technical discourse on nutrition surveillance started decades ago, and the first technical guidelines were proposed in mid-1970s. In spite of this long history, little evidence and consensus exists on the best methods for conducting nutrition surveillance, and on the validity of data produced by these approaches. Multiple nutrition surveillance systems exist in humanitarian settings; however, the validity and usefulness of data produced by these systems are often questionable. In this paper, we outline and define five major methodological approaches to collecting child anthropometric data through surveillance: repeated surveys, community-based sentinel sites, mass screenings, admission data from feeding centers, and data from health clinics. We discuss outstanding methodological and practical challenges with direct implications for quality, validity, and interpretability of collected data and highlight comparative advantages and disadvantages of different methods. We also propose ways forward to building a better evidence base by documenting the strengths and limitations of different approaches, with the eventual goal of achieving consensus on the best ways to collect anthropometric data through surveillance.