doc - Malaria Indicator Surveys

Malaria Indicator Survey
Guidelines for Sampling for the Malaria Indicator Survey
The DHS Program
Rockville, Maryland
March 2016
Table of Contents I. General principles for sampling for Malaria Indicator Surveys 3
II. Target population 5
III. Survey domains 6
IV. Sampling frame 7
V. Stratification 9
VI. Sample size determination 10
VII. Stratum sample allocation 13
VIII. A two-stage sample selection procedure 15
IX. Size of the sample taken per EA 16
X. Household listing operation 17
XI. Segmentation, mapping, and listing 18
XII. Household selection 19
XIII. The household interviews 20
XIV. DATA COLLECTION WITH A TABLET COMPUTER 21
XV. WEIGHTING THE SURVEY DATA 23
References 25
I. General principles for sampling for Malaria Indicator Surveys
ALL LARGE-SCALE SAMPLING ACTIVITIES SHOULD BE GUIDED BY A NUMBER OF GENERAL
PRINCIPLES TO ACHIEVE CONSISTENCY AND THE BEST QUALITY IN SURVEY RESULTS.
THIS MANUAL PRESENTS GENERAL GUIDELINES ON SAMPLING FOR THE MALARIA
INDICATOR SURVEY (MIS), ALTHOUGH SOME MODIFICATIONS MAY BE REQUIRED FOR
COUNTRY-SPECIFIC SITUATIONS. THIS MANUAL IS BASED ON THE DEMOGRAPHIC AND
HEALTH SURVEY SAMPLING AND HOUSEHOLD LISTING MANUAL.[1]
Survey Coverage
An MIS sample should cover 100 percent of the target population. The target
population typically depends on malaria endemicity (see Section II below),
but may also be based on program-targeted areas. The target population may
thus be the entire country, all malarious areas for a national survey, or
selected regions or malaria-program areas for a sub-national survey. The
general sampling principles are the same for each type of survey. For both
national and sub-national surveys, exclusions may be necessary because of
extreme inaccessibility.
Probability Sampling
Probability sampling must be used. A probability sample is defined as one
in which the units are selected with known and nonzero probabilities. This
is the only way to get unbiased estimation and to be able to evaluate the
sampling errors. The term excludes purposive sampling, quota sampling, and
other uncontrolled non-probability methods because they cannot provide
precision and/or confidence evaluation of survey findings.
Pre-existing Sampling Frame
A probability sample can only be drawn from an existing sampling frame that
provides a complete list of statistical units covering the target
population. Since the construction of a new sampling frame is likely to be
too expensive, an MIS should use an adequate pre-existing sampling frame.
This is possible for most countries where there have been population
censuses in recent years. However, an evaluation of the quality and the
accessibility of the frame should be part of the protocol of the survey.
This may require the cooperation of the country's national bureau of
statistics. In the interest of economy and coordination, an MIS could be
integrated with an ongoing national survey program. However, as the
sampling frame may be limited to malaria endemic areas or program-targeted
areas, local assistance in identifying areas for potential exclusion based
on malaria endemicity or targeting is advisable (see Sections III and IV
below).
Simplicity of Sampling Design
In large-scale surveys, non-sampling errors are usually the most important
sources of error and are expensive to control and difficult to evaluate. It
is important to minimize this type of error in survey implementation.
Therefore, the sampling design for MIS should be as simple and
straightforward as possible to facilitate accurate implementation. ICF
International's experience with Demographic and Health Surveys (DHS) shows
that a two-stage cluster sampling design is appropriate, as discussed in
Section VIII of this manual.
Pre-selected Households
To prevent bias, the standard MIS recommends that households be pre-
selected in the central office prior to the start of fieldwork rather than
by teams in the field. The interviewers are asked to interview only the pre-
selected households; no changes or replacements are allowed in the field.
To perform pre-selection of households, a complete list of all residential
households in each of the selected sample clusters is necessary. This list
is usually obtained from a household listing operation conducted before the
main survey.
In the sections that follow, the general MIS policy is described in
relation to a number of specific aspects of sampling design and
implementation.
II. Target population
MIS IS DESIGNED TO MEASURE ROLL BACK MALARIA (RBM) CORE POPULATION-BASED
MALARIA INDICATORS. INFORMATION NEEDED TO COLLECT THESE INDICATORS COME
FROM HOUSEHOLD INTERVIEWS (FOR ITN AND IRS INDICATORS) AS WELL AS FROM
INTERVIEWS WITH WOMEN OF REPRODUCTIVE AGE (FOR IPTP AND CASE MANAGEMENT
INDICATORS). BIOMARKER TESTING IS ALSO TYPICALLY DONE ON ALL CHILDREN 6-59
MONTHS OF AGE IN THE HOUSEHOLD (FOR ANEMIA AND PARASITEMIA PREVALENCE
ESTIMATES).
The target population for households and individuals is limited to those at
risk for malaria. Therefore, the target population of individuals for MIS
is defined as all women of reproductive age (15-49 years old) and all
children under five years of age living within malaria endemic or epidemic-
prone areas.
Considerations for countries with varied malaria transmission are discussed
in Sections III and IV.
III. Survey domains
TO COMPARE THE SURVEY RESULTS FOR DIFFERENT HOUSEHOLD CHARACTERISTICS (SUCH
AS URBAN AND RURAL AREAS, DIFFERENT ADMINISTRATIVE OR GEOGRAPHICAL REGIONS,
HIGH- AND LOW-INTENSITY MALARIA TRANSMISSION REGIONS, HIGH AND LOW LEVELS
OF MALARIA PROGRAMMATIC ACTIVITY, ETC.), THE TARGET POPULATION IS
SUBDIVIDED INTO STUDY DOMAINS OR MAJOR SEGMENTS OF THE POPULATION FOR WHICH
SEPARATE STATISTICS ARE NEEDED. IT IS EXPECTED THAT INDICATORS WILL BE
TABULATED AT THE NATIONAL LEVEL AS WELL AS AT THE SURVEY-DOMAIN LEVEL.
For a national survey for countries with endemic and/or epidemic-prone
malaria throughout, the coverage should include the entire national
territory without omission unless there are justifiable reasons for
excluding certain areas. For countries that contain regions without malaria
transmission that are excluded from the survey, these regions should
constitute a coherent domain. A survey from which a number of scattered
zones have been excluded is difficult to interpret and use. If a malaria
program implements very different levels of programmatic activity from one
malarious area to the next, then "level of programmatic activity" could be
a characteristic used to define survey domains. Thus, a survey might
measure malaria indicators separately for different parts of the country
with different levels of program activity (and a single national estimate
could also be calculated).
In order for survey estimates to be reliable at the domain level, it is
necessary to ensure that the size of the target population in each survey
domain is sufficient, especially when desired levels of precision are
required for particular domains. For a design domain, adequate sample size
is achieved by allocating the target population at the survey design stage
into the requested design domains, and then calculating the sample size for
the specific design domains by taking the precision required into account.
If domain-level estimates are required, it is best to avoid a large number
of domains because otherwise a very large sample size will be needed which
has logistic and quality implications for the survey. The number of domains
and the desired level of precision for each must be taken into account in
the budget calculation and assessment of the implementation capabilities of
the implementing organization. The total sample size needed is the sum of
sample sizes needed in all exclusive (first level) domains.
IV. Sampling frame
A SAMPLING FRAME IS A COMPLETE LIST OF ALL SAMPLING UNITS THAT ENTIRELY
COVER THE TARGET POPULATION. THE EXISTENCE OF A SAMPLING FRAME ALLOWS A
PROBABILITY SELECTION OF SAMPLING UNITS. FOR A MULTI-STAGE SURVEY, A
SAMPLING FRAME SHOULD EXIST FOR EACH STAGE OF SELECTION. THE AVAILABILITY
OF A SUITABLE SAMPLING FRAME IS A MAJOR DETERMINANT OF THE FEASIBILITY OF
CONDUCTING AN MIS. THIS ISSUE SHOULD BE ADDRESSED IN THE EARLIEST PLANNING
FOR A SURVEY. A SAMPLING FRAME COULD BE AN EXISTING SAMPLING FRAME, AN
EXISTING MASTER SAMPLE, OR A SAMPLE OF A PREVIOUSLY EXECUTED SURVEY OF
SUFFICIENTLY LARGE SAMPLE SIZE THAT ALLOWS FOR THE SELECTION OF SUBSAMPLES
OF THE DESIRED SIZE FOR THE MIS. THE BEST FRAME IS THE LIST OF ENUMERATION
AREAS (EAS) FROM A RECENTLY COMPLETED POPULATION CENSUS.
In most cases, an area sampling frame, which is a list of the EAs in a
complete census, is available. This list should be thoroughly evaluated
before it is used. The sampling frame used for the MIS should be as up-to-
date as possible. It should cover the whole country or subnational area
included in the survey, without omission or overlap. Maps should exist for
each area unit or at least groups of units with clearly defined boundaries.
Each area unit should have a unique identification code or a series of
codes that, when combined, can serve as a unique identification code. Each
unit should have at least one measurement of size estimate (population
and/or number of households). If other characteristics of the area units
(e.g., socioeconomic level) exist, they