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Sample Selection: SAFE Project
Study Design• 3-Level Multi Site Cluster Randomized Trial (CRT) with
power=0.80; alpha=0.05; and r=0.01
• 3 arms with different combinations of intervention, to be measured at baseline and endline in 18 months apart
Arm 1 Arm 2 Arm 3
• Clinic • Clinic • Clinic
• Community campaigning
• Community campaigning
• Community campaigning
• Female groups • Female groups
• Male groups
Why 3 arms?• A comparison between
Arms 1 and 2 will inform the added advantage of male groups on top of clinic, community campaigning and female groups
• A comparison between Arms 3 and 2 will inform the added advantage of female groups on top of clinic and community campaigning
Arm 1 Arm 2
• Clinic • Clinic
• Community campaigning
• Community campaigning
• Female groups • Female groups
• Male groups
Arm 2 Arm 3
• Clinic • Clinic
• Community campaigning
• Community campaigning
• Female groups
All common intervention components across arms, i.e.,
clinic, community campaigning and female group sessions
must be similar across arms of all sitesfor ensuring comparability
Standardization of intervention components
Study Subjects and Sample SizeAge group and sex
Marital status
Effect variable
MDES Clusters for 3 arms
Cluster size (N)
Cluster size (N) with 20%
over-sampling
No. of sites (K)
Sample-3 arms
15-19 females
Married; Unmarried
Marriage 45% 51 15 18 3 2754
20-29 females
Married; Unmarried
Violence exposure 55% 27 15
183 1458
18-35 males
Married; Unmarried
SRHR Knowledge
and attitudes
55% 27 1518
3 1458
Total Female sample (2754+1458) 4212
Total Male sample 1458
Total sample (2754+1458+1458) 5670
Process of sample selection• First, identify the three study sites, each with one MS clinic
• All sites should have similar type of MS clinics (for instance, 3 UPHCP referral clinics have been selected for the project)
• Each site needs to have at least 51 clusters of young females (YF) and 27 clusters of adult females (AF)
• Adult female clusters can be merged with YF clusters if each cluster has at least 18 x 2= 36 households; because only one respondent (YF/AF) will be interviewed from each selected household (Caution: This rule does not apply for conducting group sessions)
• Thus, each cluster need to have minimum 36 hhs, preferably 50 hhs to avoid refusal/drop out
Continued….
Process of sample selection• Males cannot be interviewed from the same cluster as that of
the females for the safety of the females
• Therefore, additional 27 clusters need to be selected from each site
• Thus, each site requires a total 78 (Female: 51 + Male: 27) non-contaminated clusters
• 78 clusters will be randomly assigned to the three arms, with 26 clusters for each arm
How to form a cluster• Cluster, preferably, should have geographical
boundary• Cluster, preferably should have
natural/administrative characteristics binding them into a group; for instance, a village or a para can be a cluster, which however, is difficult to achieve in a slum setting
• Clusters need to be identified and marked during enumeration/listing
• Either natural factors or houses should be identified as buffer zone between clusters to control contamination
Understanding the temporary settlement/slum setting
Three study sites include 3 UPHCP referral clinics-
• Mohammadpur Landmark: Sikder Medical, PoolparNo. of slums-8 ; Population-30,285
• BashaboLandmark: Buddha MandirNo. of slums-7; Population-14,200 (MS will identify more slum population)
• MohakhaliLandmark: Mohakhali FlyoverNo. of slums-5; Population-30,500
Understanding the temporary settlement/slum setting
Three study sites include 3 UPHCP referral clinics-
• Mohammadpur Landmark: Sikder Medical, PoolparNo. of slums-8 ; Population-30,285
• BashaboLandmark: Buddha MandirNo. of slums-7; Population-14,200 (MS will identify more slum population)
• MohakhaliLandmark: Mohakhali FlyoverNo. of slums-5; Population-30,500
Minimum population requirement per site
Each site must have 25,000-30,000 population(5,000 to 6,000 households) because---
•78 clusters x 50 households= 3,900 HHs•3,900 HHs x 5 members = 19,500 population•Additional 2,000 HHs with 10,000 population are needed for creating buffer zone among clusters
Note: 19,500 population is enough to have 918 young females of 15-19 years [19500 x 10% 15-19 years old x 50% female]
Each of the three site has 1 clinic and 5 to 8 slums
Mohammadpur clinic [Poolpar]
Bashabo clinic [Mandir]
Mohakhali clinic [Flyover]
Site-1 Site-2 Site-3
Slum 1
Slum 2
Slum 3
Slum 4
Slum 5
Identification of clusters across 3 armsMohakhali Clinic
Arm 1
Arm 2
Arm 3
Re-randomization
• Background characteristics, especially proportion of married girls and level of education should be similar across 3 arms of each site
• Since ICDDR,B will enter data of the listing, after randomly assigning the clusters and looking into the differences in terms of marital status of young females, arms may be reassigned through rerandomization
Scopes for contamination
• Contamination by participation- females subjects from arm 3 may take part in or recruited into female groups of arms 1 or 2; similarly male subjects from arms 2 and 3 may take part in male groups of arm 2
• Contamination by diffusion- geographically proximate clusters with people having regular and meaningful social interaction may contaminate by diffusion
Measures to reduce contamination• Contamination by participation
– Each hh will be marked with hh and cluster numbers; – Frontline staff will be cautioned and supervised so
that they do not recruit subjects from inappropriate arms (for example, females from arm 3; and males from arms 2 and 3)
• Contamination by diffusion– geographical and buffer hhs will be identified; – social groups centering on leaders’
houses/landmarks/shops will be identified and kept in the same cluster to reduce the diffusion through social networking
Clusters for survey and groups for intervention per site across 3 arms
Mohakhali ClinicArm 1
Arm 2
Arm 380 FGs (50 YF + 30 AF)
44 MGs (50 YF + 30 AF)
26 FCs (17 YF + 9AF)
9 MCs
80 FGs (50 YF + 30 AF)
26 FCs (17 YF + 9AF)
9 MCs
26 FCs (17 YF + 9AF)
9 MCs
Number of female and male groupsGroup characteristics
Arm 1 Arm 2 Arm 3 Total groups in each site
Total groups in 3 sites
• 10-14 female groups 16 16 - 32 96
• 15-19 female groups 50 50 - 100 300
• 20-29 female groups 30 30 - 60 180
Total female groups 192 576• 18-35 male
groups 48 - - 48 144
Total male groups 48 144
Groups can be formed according to marital status for 15-29 years old.