Module 8 Survey sample builder

Module 8 Survey sample builder (SSB)

TAS

Global Programme to Eliminate Lymphatic Filariasis (GPELF)

Training in monitoring and epidemiological assessment of mass drug administration for eliminating lymphatic filariasis

Module 8 Survey sample builder


Learning objectives

Slide 2

By the end of this module, you should understand:

1. how to use the survey sample builder to: determine the survey design select random clusters and children or households

2. the protocol for TAS


Overview

The survey sample builder Determining the survey design Selecting randomized clusters Selecting randomized children or households Protocol for TAS

Slide 3


Survey sample builderThe survey sample builder is a Microsoft Excel tool that can be used to (i) automate calculations for determining the appropriate survey design and (ii) facilitate random selection of clusters and children or households from a list of randomized numbers.

Slide 4

School

CensusCluster-based Systematic

School

Child Child

Community


Enumeration area

Household Household

Survey design

Random selection

Sample size and critical cut-off

Evaluation unit


Preparation before sample selectionSchool-based survey

Slide 5

Communicate with the ministry of education to obtain a comprehensive list of all primary schools in the defined EU. Ideally, the list of schools will be ordered according to

geographical proximity rather than alphabetically. This will allow better geographical representation of the selected schools in the EU.

Obtain an average non-response rate for the schools in the EU, if available. The non-response rate gives an estimate of the non-participant

rate and should include school absenteeism, refusals and inability to collect sufficient blood for diagnostic testing.


Preparation before sample selectionCommunity-based household survey

Slide 6

Census enumeration areas are recommended as clusters if cluster sampling is used; enumeration areas are usually the smallest areas for which census data are available.

Obtain a list of all enumeration areas in the EU. Ideally, the enumeration areas will be listed according to

geographical proximity rather than alphabetically.

Obtain enumeration area census maps. These maps can often be obtained from the census department

or bureau of statistics. A fee may be charged to obtain these maps.

Module 8 Survey sample builder (SSB)Slide 7

Available for download at http://www.filariasis.us./resources.html

Determining the survey design






Survey sampling method determined by data entered into

programme



Once the appropriate survey design has been determined, the survey sample builder facilitates selection of clusters and children or households by generating a list of randomized numbers.

Slide 11

School


School

Child Child

Community


Enumeration area

Household Household

Survey design

Random selection

Sample size and critical cut-off

Evaluation unit

Selecting randomized clusters and children or households


Selecting randomized clusters

Slide 12

Cluster sampling requires a minimum of 30 schools or enumeration areas in which children are selected.1. Obtain a comprehensive list of all primary sampling units (i.e.

schools, enumeration areas) in the evaluation unit.

2. Number them, preferably in order of geographical proximity as opposed to alphabetical order to achieve better geographical distribution of the evaluation unit.

3. Once all sampling units have been assigned a number, click the “Randomize” button.

4. Once the survey design has been determined, a list of random numbers (e.g. 10, 23, 36, 49 …) is generated. Select the schools or enumeration areas in the list according to the random numbers (i.e. 10th, 23rd, 36th, 49th …).



Slide 13

Total number of EAs: 487No. of EAs (clusters) to be sampled: 37

Directions: Obtain a comprehensive list of all the primary sampling units (i.e. Schools or EAs) in the EU and number them, preferably in order of geographic proximity. Once all sampling units have been assigned a number, double check that the values listed below are correct and click the "Randomize" button. When you are finished you can click "Return to Previous Page" to go back.

Randomize

Return to Previous Page

A list of random numbers can be generated to facilitate the selection of clusters to be included.

The following schools or enumeration areas have been selected for your study: 10

233649627689

102….



Slide 14

Selection of 5–10 additional clusters is recommended as a contingency plan if the sample size falls considerably short of the target after all the clusters have been surveyed. Additional clusters should be selected from a list of all remaining

clusters, excluding those that have already been chosen. The same random selection process used for the original clusters should be used.

The survey sample builder allows selection of additional clusters.


Selecting randomized children or households

Slide 15

After selection of randomized clusters in cluster sampling or after choosing systematic sampling, children (in school-based surveys) or households (in community-based surveys) are selected randomly.

The survey sample builder calculates the appropriate sampling interval.

The survey sample builder also calculates a random starting number and the sampling interval (inverse of the sampling fraction) to generate two numbered lists (A and B) to guide the actual selection of schoolchildren or households

For school-based surveys, lists A and B are used to select the children to be tested.

For community-based surveys, lists A and B are used to select the houses in the enumeration areas to be sampled.


Selecting randomized children or households

Slide 16

In this example, the team chose list A; therefore, the first, third, fourth, fifth … house on the list or map will be selected.

Every 6- and/or 7-year-old child in the house should be tested. The same list should be used throughout the survey.


Example 1

Slide 17

Net school enrolment ratio: 78%

Primary vector: Culex

Population of students in target grades: 18 945

Total number of primary schools: 386

Estimated non-response rate: 15%


Example 1. Survey design

Slide 18

Country: Example 1Name of EU: Example 1Primary Vector: Anopheles, Culex, or Mansonia

Demographic data on EU (provided by user)

Population of students in target grade(s):18,945

Total number of schools: 386 Avg. number of students in target grade(s) per school: 49*Note, if any of the above information is incorrect, click on the 'Back to "Start Here"' button and then click 'edit EU information'

Cluster Survey of School Entrants Survey Sampling Methodology (calculated by program)

Sample Size for Cluster Design 1,552Number of Clusters1 38

Sampling Fraction (of children within the schools)1Test all children in the target grade(s)

Sampling Interval (of children within the schools)1N/A

Critical Cut-off (maximum # positive ICT/Brugia Rapid results allowable for country to "Pass") 18

1Based on a 15% absentee rate


Example 1. Randomized cluster selection

Slide 19

Directions: Obtain a comprehensive list of all the primary sampling units (i.e. schools or enumeration areas) in the evaluation unit, and number them, preferably in order of geographical proximity. Once all sampling units have been assigned a number, double-check that the values listed below are correct, and click the "Randomize" button. When you have finished, you can click "Return to previous page”.

Total number of schools: 386No. of schools (clusters) to be sampled: 38

The following schools have been selected for your study:8

1829394959697990

100110

…


Example 1. Randomized cluster selection

Slide 20

School name1 Woodridge Elementary2 Lakeside Elementary3 Shadow Rock Elementary4 Austin Elementary5 Idlewood Elementary6 Henderson Mill Elementary7 Stone Mill Elementary8 Rockland Elementary9 Sage Elementary

10 Oak Grove Elementary11 Brockett Elementary12 Princeton Elementary13 Chestnut Elementary14 Rockbridge Elementary15 Dresden Elementary16 Midvale Elementary17 Columbia Elementary18 Pine Ridge Elementary19 Flatrock Elementary20 Snapfinger Elementary…

The following schools have been selected for your study:

81829394959697990

100110

…


Example 2

Slide 21


Primary vector: Anopheles


Total number of enumeration areas: 284




Slide 22

Country: Example 2Name of EU: Example 2Primary Vector: Anopheles, Culex or Mansonia


Population of 6-7 yrs:23,128

Total number of EAs: 284 Avg. population 6-7yrs per EA: 81*Note, if any of the above information is incorrect, click on the 'Back to "Start Here"' button and then click 'edit EU information'

Cluster Survey of Households Survey Sampling Methodology (calculated by program)

Sample Size for Cluster Design 1,552Number of Clusters1 30Sampling Fraction (of children within the EAs)1

0.75Sampling Interval (of children within the EAs)1

1.34Critical Cut-off (maximum # positive ICT/Brugia Rapid results allowable for country to "Pass") 18



Example 2. Randomized selection of households

Lists corresponding to the houses selected for sampling out of all houses in the selected enumeration area

The random number used to generate these lists is: List A List B

0.775367533 1 13 24 45 57 68 89 9

11 1012 1213 1315 1416 16… …

1 2 3 4 5 6

10 9 8 71112


Example 3

Slide 24


Primary vector: Aedes


Total number of primary schools: 24




Slide 25

Country: Example 3Name of EU: Example 3Primary Vector: Aedes


Population of students in target grade(s):2,814

Total number of Schools: 24

Avg. number of students in target grade(s) per school: 117*Note, if any of the above information is incorrect, click on the 'Back to "Start Here"' button and then click 'edit EU information'

Systematic Sample of School Entrants Survey Sampling Methodology (calculated by program)

Sample Size for Systematic Sample 1172

Sampling fraction (children within each school)1

0.49Sampling interval (children within each school)1

2.04Critical Cut-off (maximum # positive ICT/Brugia Rapid results allowable for country to "Pass") 7


Will visit every school in the

evaluation unit


Protocol for TAS

Slide 26

Define EU Determine survey site and sampling strategy Calculate sample size Prepare lists

Schools (school-based survey) Enumeration areas (community-based survey)

Test selected children ICT (areas endemic for W. bancrofti) Brugia RapidTM (areas endemic for Brugia spp.)

Interpret results on basis of critical cut-off


Exercise

Slide 27

Using population data from the evaluation unit(s) defined in the ‘Evaluation unit’ module:

Use the survey sample builder to define:

the appropriate survey design

the sample size needed

the number of clusters needed for the survey

the sampling fraction

the sampling interval

Use the survey sample builder to:

select clusters to be included (if necessary)

generate lists A and B (if necessary)

Documents

Module 8 Survey sample builder