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CRVS tools

Verbal autopsy sampling strategy tools

Many low-income countries are considering introducing verbal autopsy (VA) as an integral part of their civil registration and vital statistics (CRVS) systems in order to generate population level cause of death statistics in those parts of the country where there is currently no possibility for medically certified cause of death assignment. There are presently at least 13 countries 1 implementing VA whereby these countries are establishing their technical, process and systems integration needs prior to launching national-scale VA implementation.

The primary purpose of VA in CRVS is to provide statistical trend data at population (not individual) level on the cause-specific mortality fractions for monitoring major health interventions, universal health coverage and sustainable development goals. Such data do not require a verbal autopsy on every death. A sample of deaths is sufficient. But how large should the sample of deaths be? And how should those deaths be selected to ensure results are representative? This strategic guidance document and associated tool are intended to assist such countries.

1 Bangladesh, Colombia, Ghana, Kenya, Morocco, Myanmar, Papua New Guinea, Philippines, Rwanda, Tanzania, Solomon Islands, Sri Lanka, Zambia.

What are some of the key principles in this strategy?

The most important driving principles behind the VA Sampling Strategy and Tool are:

  1. Verbal autopsy is not a substitute for medically certified cause of death. It is intended for use where there is no physician, and for generating population level data on proportions and rates of cause-specific mortality. Therefore this guidance is written for countries where a substantial share of the population experiences mortality outside of health facilities and in the absence of medical attendance at death. The tool factors into its calculations the understanding that VAs will be done primarily on community deaths, i.e. those occurring outside of health facilities, even though some deaths occurring in health facilities may not receive a medically certified cause.
     
  2. Verbal autopsies do not need to be conducted on all deaths, but only on an appropriately large random sample of deaths. It is logistically and operationally inefficient to do random VA sampling on individual deaths. Therefore cluster sampling is recommended whereby the cluster unit needs to be decided. The principle we propose is that the minimum cluster sample unit should be the catchment area of deaths that can be reached by a single trained and equipped VA interviewer. Such geographic areas tend to be of a size in which each interviewer would have a work load of 2 to 4 VAs per month, and tend to be approximately the size of census or CRVS enumeration areas (e.g. population sizes between 2,000 and 20,000). This is the minimum cluster unit size. However, some implementation designs may decide on larger cluster units with larger populations and multiple VA interviewers working across the cluster.
     
  3. Sampling should be driven by careful a priori decisions on the levels of disaggregation that will be applied in data analysis. At a minimum, the sample size should be adequate to allow analysis of the leading causes of death separately for males and females, and if possible, for the major age groups of neonates, children and adults.
     
  4. Strategic consideration must be given to further geographic disaggregation of analyses (urban/rural, and sub-national (regional/provincial)), especially in countries with decentralized governance of health and social services.
     
  5. Statistical representation requires not just the correct minimum sample size in terms of number of clusters (and VAs) to address the above analyses, but also the drawing of that sample through a random sample of the cluster units from an appropriately constructed sample frame. This Guidance provides a methodology for both calculating the size, and doing random cluster sampling. Given it is highly likely that at some point countries will wish to have disaggregated analyses at least to state, provincial or regional level, we have designed the calculator to be based on an approach of single-stage stratified random cluster sampling proportional to population size. 
Who should use this guidance and tool?

This CRVS VA Sampling Strategies Guide and its associated Sample Size Calculator Tool (links below) are intended primarily for those responsible for providing high quality mortality data in countries where a decision has been made to use VA as part of the CRVS system. It allows CRVS VA managers in such countries to determine the number and location of geographic units to be sampled to detect a nationally representative change in cause specific mortality fractions or rates in populations where medical certification of cause of death is not yet feasible.

When should the Guidance be applied?

The Guidance and the Tool (links below) are expected to be of value to countries who have concluded the pre-test or pilot phases of their VA implementation and who have established the technical, process, and incremental cost considerations with regard to VA implementation at scale. 

What questions does the Guidance address?

The Guidance addresses four key issues regarding the implementation of CRVS VA at national scale:

  1. What are the key logistical considerations to make with regard to the definition of an operational CRVS VA cluster?
     
  2. What are the key strategic considerations to decide with regard to the level of disaggregation at which analyses will be conducted (sex, age, urban-rural, sub-national administrative, trend period, etc.)?
     
  3. What is the minimum number of sample units (clusters) and number of VAs needed given an acceptable uncertainty range for detecting significant CSMF changes over time? Or alternatively, what is the uncertainty range for detecting significant CSMF changes over time given a number of clusters sampled?
     
  4. How should the required sample clusters be selected from the national sample frame?
How can the Guidance be used?

The tool allows CRVS managers to:

  1. Determine the required sample size for a national or sub-national system given an acceptable uncertainty range for detecting significant CSMF changes over time.
     
  2. Determine the uncertainty range for detecting significant CSMF changes over time given the current or planned deployment of VA.
How does this Guidance help?

The relationship between the number of VAs conducted and the resulting uncertainty range for detecting significant CSMF changes over time of various levels of CSMF is not intuitively easy to appreciate. For example, a given number of VAs conducted in a relatively small number of very large clusters will give wider uncertainty ranges compared with those conducted in a larger number of smaller CRVS-Verbal Autopsy Sampling Strategies for Representative VA Implementation: A Practical Guide Preface 12 clusters. This has operational and cost implications. Hence, this tool should be used in concert with the CRVS VA Costing Tool. Using both tools will be helpful in making key decisions with regard to strategies for scaling up CRVS VA in national systems.


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CRVS-VA sample size calculator tool

The purpose of this package of a two part guidance document and its companion sample size calculator Tool is to assist countries with scale up and rollout planning for the application of verbal autopsy (VA) as a function of a national civil registration and vital statistics (CRVS) system. Users of the package will include those tasked with designing and managing the CRVS-VA system. The package is intended to be used after pre-testing and pilot phases during which the processes, methods and possibly costing of the CRVS-VA system are perfected and established, and before the scale-up and rollout phase.

Download resource (588KB)
More Info

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Sampling strategies for national scale CRVS-VA planning: Guidance document and sample size calculator tool

The purpose of this package of a two part guidance document and its companion sample size calculator Tool is to assist countries with scale up and rollout planning for the application of verbal autopsy (VA) as a function of a national civil registration and vital statistics (CRVS) system. Users of the package will include those tasked with designing and managing the CRVS-VA system. The package is intended to be used after pre-testing and pilot phases during which the processes, methods and possibly costing of the CRVS-VA system are perfected and established, and before the scale-up and rollout phase.

Download resource (3.30MB)
More Info

Authors: University of Melbourne, Swiss Tropical and Public Health Institute, Vital Strategies, London School of Hygiene and Tropical Medicine, CDC

Publication date: May 2018

Resource type: CRVS resources and tools

Related resources: CRVS-VA sample size calculator tool


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