Determining Sampling Methods CEI Implementing the Reproductive Health Assessment Toolkit for Conflict-Affected Women November 5, 2006

Objectives At end of session, you will be able to: Understand importance of sampling Describe advantages/disadvantages of random and cluster sampling Obtain hands on sampling experience

What is Sampling? The procedure by which some members of a population are selected as representative of the entire population

Importance of Sampling Good sampling = representative data!! –Make reasonable inferences Decreases costs Speeds up data collection Balance feasibility and precision

Toolkit Sampling Sampling unit = households (HH) One woman of reproductive age (WRA) per HH Choose random or cluster sampling Modify based on needs

Area

Geographic Bounds Well-defined –Refugee or IDP camp –Groups of camps –Villages or towns where displaced people live Use a map

Random Sampling AdvantageDisadvantage Random More precise Smaller sample size Complete HH listing Could use more resources More travel/time

Cluster Sampling AdvantageDisadvantage Cluster No/incomplete HH listing Could use less resources Less travel Less precise Larger sample size

Random vs Cluster AdvantageDisadvantage Random More precise Smaller sample size Complete HH listing Could use more resources More travel/time Cluster No/incomplete HH listing Could use less resources Less travel Less precise Larger sample size

Random Sampling Assumptions: –Prevalence rate of 50% –95% confidence intervals +/- 5% –Response rate of 80% 400 completed interviews  must sample 500 HH

Random Sampling Steps Step 1. Obtain HH lists Step 2. Identify HHs and select sample HHs to be surveyed Step 3. Select one WRA with each selected HH to be surveyed

Sample Household List ID#NameAgeFamily size # WRADate of arrival 2416X316211/27/ X26418/22/ X43414/21/ X53507/1/ X284211/20/ X34517/5/1998 Household removed before selection because no WRA

Practice Exercise: Random

Random: Table 1 CampHouseholdsHousehold proportion Sample size Camp 1367 Camp 2405 Camp 3245 Camp 4271 Camp 5350 Total /1638 =22.4%

Random: Table 1 CampHouseholdsHousehold proportion Sample size Camp /1638 = 22.4% Camp /1638 = 24.7% Camp /1638 = 15.0% Camp /1638 = 16.5% Camp /1638 = 21.4% Total %.224 x 500= 112

Random: Table 1 CampHouseholdsHousehold proportion Sample size Camp /1638 = 22.4%.224 x 500= 112 Camp /1638 = 24.7%.247 x 500= 124 Camp /1638 = 15.0%.150 x 500= 75 Camp /1638 = 16.5%.165 x 500= 83 Camp /1638 = 21.4%.214 x 500= 107 Total %501

Random Numbers Table OR use computer applications For both random and cluster Example: Randomly select 112 HHs from 367 HHs for Camp 1. –How many digits -> , need 3 digits –Choose a direction -> decide to go right –Choose starting point –Read the number of digits –Repeat until 112 HHs selcted

Random Numbers Table ABCDE (discard not in range)

Random Numbers Table ABCDE HH is selected for sample

Cluster Sampling Can not guarantee precision Assumptions: –Response rate of 80% –At least 25 clusters with 25 HH in each Probability proportional to size (PPS) 500 completed surveys  so sample 625 HHs

Cluster Sampling Step 1. Define clusters within geographic boundaries Step 2. Determine the number of HHs within each cluster Step 3. Select the clusters to be surveyed Step 4. Select the HHs within each cluster to be surveyed Step 5. Select one WRA within each selected HH to be surveyed

Practice Exercise: Cluster

Cluster: Step 3 ClusterHH in clusterCumulative # of HHs Range (etc... )

Cluster: Step 3 Sampling interval = cumulative # of HH divided by 25 clusters –Ex: 970/25 clusters = 39 (sampling interval) Randomly select number within sampling interval range –Ex: = 31 is starting number Find where this number falls within range and cluster selected

Cluster: Step 3, select 1 st cluster ClusterHH in clusterCumulative # of HHs Range (etc... ) falls within range Cluster 2 selected for sample

Cluster: Step 3 Add sampling interval to first number: –Ex: = 70 Find where this number falls within range and cluster selected Continue until 25 clusters selected

Cluster: Step 3, select 2 nd cluster ClusterHH in clusterCumulative # of HHs Range (etc... ) falls within range Cluster 3 selected for sample

Cluster: Step 3, select 3 rd cluster ClusterHH in clusterCumulative # of HHs Range (etc... ) =109 falls within range Cluster 3 selected again for sample

Random vs Cluster AdvantageDisadvantage Random More precise Smaller sample size Complete HH listing Could use more resources More travel/time Cluster No/incomplete HH listing Could use less resources Less travel Less precise Larger sample size

DRH Technical Assistance Review sampling plan Consult on different sampling methods

Reproductive Health Assessment Toolkit for Conflict-Affected Women