rapid assessment of drinking-water quality in the republic of tajikistan

Table 2.2
Country-specific survey design for Tajikistan a
Step
Method described in
project handbook
Survey design in Tajikistan
Justification for variation from
handbook method
1 Calculate sample size.
(= 1600).
In total, 1780 sampling points were
included in the survey: 1620 from source
waters and 160 from households.
Because of rounding during secondary
stratification, the sample size for source
waters is 1606. This number increased
to 1620, owing to a mistake in the
sampling plan.
2 Primary stratification.
Proportional weighting by
technology type, based on
% of population served.
(Note: only technologies
serving >5% of the
population were included
in the survey).
3 Secondary stratification.
Proportional weighting by
broad areas (based on the
number of water supplies
across the country).
The study area covered the whole of the
Republic of Tajikistan.
Two technologies served more than 5% of the
population, which were therefore selected in
the primary stratification:
utility piped supplies (1286 sample points);
protected springs (320 sample points).
Broad areas correspond to oblast
administrative areas. Four broad areas were
selected (see also):
RRS & Dushanbe : 253 utility piped
supplies and 108 protected springs;
Khatlon: 173 utility piped supplies and 103
protected springs;
Sughd: 205 utility piped supplies and 46
protected springs;
GBAO: 12 utility piped supplies and 63
protected springs.
To achieve the required number of
sample points in utility piped supplies:
the zone size was reduced from 5000
to 2500 people per zone;
a repeat sampling approach was
adopted (i.e. 643 sampling points were
selected, but each point was
tested/inspected twice).
4 Define clusters (size and
number). Based on
supplies that can be visited
in one week by one team
(cluster size).
5 Define and select
sampling units. These are
the areas from which
clusters are selected by
proportional weighting.
6 Select clusters and
individual water supplies.
These are the supplies that
will be assessed for water
quality.
In total, 53 clusters were identified. As the
30 clusters for utility piped supplies were
visited twice, this resulted in 83 team-weeks
or 21 project-weeks with 4 teams. The
clusters in the broad areas were defined as
follows (cluster size, number of clusters):
Dushanbe and RRS: utility piped supplies
(30, 9); protected spring (20, 6).
Khatlon: utility piped supplies (20, 9);
protected spring (15, 7).
Sughd: utility piped supplies (20, 11);
protected springs (15, 4);
GBAO: utility piped supplies (12, 1);
protected springs (12, 6).
Rayons were used as the sampling units for
the third administrative level. The results of
proportional weighting are given in Annex 4.
Sampling plans were prepared for the field
teams (e.g. Annex 6). They provided details
on the rayons from which clusters or supplies
were to be selected, and on the water supply
scheme numbers to be assigned. Selection of
individual supplies/sample points was
undertaken by the field teams, after seeking
advice from the local authorities or
population.
Cluster sizes were selected for each
technology and broad area, to
adequately reflect local conditions (such
as accessibility, road and weather
conditions).
a
GBAO = Gorno-Badakhshan Autonomous Oblast. RRS = rayons under direct republican subordination.
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