1. Module 3 Evaluation unit
Training in monitoring and epidemiological assessment of mass drug administration for eliminating lymphatic filariasis
Module 3 Evaluation unit

2. Learning objectives By the end of this module, you should understand:
How to define a survey area, known as an evaluation unit (EU).

3. Overview Survey area for a TAS Defining an EU Combining IUs
Dividing IU
Geographical area of an EU

4. Sample size and critical cut-off
Survey area for a TAS
If all the data from relevant IUs confirm that they are eligible for a TAS, planning can begin.
The first step in designing a TAS is to define the survey area.
1. Survey area
Evaluation unit
2. Survey site
School
Community
3. Sampling strategy
Cluster-based sampling
Systematic sampling
Census
4. Sample size
Sample size and critical cut-off

5. Survey area for a TAS
Implementation unit (IU): The administrative unit in a country used for MDA
Evaluation unit (EU): An area selected for a TAS

6. Defining an EU
IUs within an EU can be combined, divided or remain the same, but all IUs in a country in which MDA is conducted must be included in a TAS.
IUs in an EU are usually contiguous.
All IUs in an EU should have had at least five effective rounds of MDA (i.e. ≥ 65% total population) and meet all the eligibility criteria for conducting a TAS.
All areas in the EU should have similar epidemiological features and LF transmission dynamics (e.g. epidemiological drug coverage, baseline prevalence, prevalence of Mf or Ag in sentinel and spot- check sites, principal parasites, vector abundance).
The population should not exceed 2 million.

7. Combining IUs 2 1 Endemic IU 3 MDA #1 #2 #3 #4 #5 Unit
Total population
Baseline Mf prevalence (%)
MDA coverage (%)
Sentinel site Mf prevalence (%)
(after fifth round)
Spot-check site Mf prevalence (%) #1 #2 #3 #4 #5 1
32 983
2.1 81 69 79 76 2
3.4 78 67 77 72
0.3
0.1 3
52 138
2.9 75 70 68 2 1
Endemic IU 3
MDA

8. Dividing an IU Endemic IU MDA 1 2 3 #1 #2 #3 #4 #5 1 798 234 1.8 2
Total population
Baseline Mf prevalence (%)
MDA coverage (%)
Sentinel site Mf prevalence (%)
(after fifth round)
Spot-check site Mf prevalence (%) #1 #2 #3 #4 #5
2.8 79 66 71 74 72
0.2
0.3
Endemic IU
MDA 1 2
Sub-district
Total population
Baseline Mf prevalence (%) 1
1.8 2
5.4 3
1.2 3

9. Geographical area of an EU
Although there is no upper limit to the geographical area of an EU, the following considerations should be taken into account when combining IUs:
The probability that foci of infection will be missed increases as the geographical area of the EU increases.
Covering a larger area during the survey may increase logistical requirements (e.g. transport costs).

10. Exercise
Using existing data (e.g. maps, list of IUs, population sizes, number of rounds of MDA and coverage).
Define an appropriate EU(s).
Note: Some of the data will have been reported on the ‘ELIGIBILITY’ worksheet of the TAS Eligibility and Reporting Form
Present the defined EU(s) to the group.