1. Weighting Your Data

2. General Information
Allows you to generalize your results to the entire population
Necessary for all sampled based surveys
Requirements
Scientifically selected sample
Complete documentation
High overall response rate

3. What does weighting do? It accounts for
the probability of selection within the population
non-response
distribution of the target population by age and sex
It allows one participant to represent many others

4. Probability of Selection from the Sample (Individual Weight)
Accounts for the variation in the selection probabilities in the sample
= 1/[(selection probability of cluster 1)* (selection probability of cluster 2)*(as many clusters until reach primary sampling unit)]

5. Example
There are 12 districts and 3 are randomly selected; probability of selection at district level =.25
District
Towns selected
Towns in district
Probability of selection (town)
INDIVIDUAL WEIGHT A 8 30
.27
1/(.25*.27) B 3 10
.30
1/(.25*.30) C 5 22
.23
1/(.25*.23)

6. Non-Response Non-response can cause bias
Information on response must be collected during interviews
Interview tracking form collects this information
Entered during data entry
Automatically attached to dataset with Epi Info program

7. Calculating the Non-Response Weight
Calculate non-response for each age and sex stratum
Non-response weight =
1/(response rate for age-sex stratum)

8. would be calculated for
Example
Males by age
Response Rate (RR)
Non-response weight = 1/RR
25–34
.94
1.064
35–44
.95
1.053
45–54
.87
1.149
55–64
.79
1.266
Non-response weights
would be calculated for
both men and women.

9. Population Distribution
Used to adjust the sample to the target population
"Post-stratification adjustments"
Need population information stratified by age and sex to calculate

10. Calculating Population Weight
Proportion of population/Proportion of sample
(Age-Sex of population / Total population)
(Age-Sex of sample / Total Sample)

11. Example Males by age Pop N Proportion of population (A) Sample N
Proportion of sample (B)
Weight
= A/B
25–34
2,000
.200 30
.075
2.667
35–44
1,760
.176 40
.100
1.760
45–54
1,440
.144 50
.125
1.152
55–64
1,600
.160 60
.150
1.067
Total
10,000
400
Post stratification would be calculated for males and females

12. Overall Weight for Individual Steps
W1: Individual weight
W2s1: Non-response weight
W3: Population weight
WStep1= W1*W2s1*W3
WStep2= W1*W2s2*W3
WStep3= W1*W2s3*W3

13. Weighting and STEPS Tools to help calculate weights STEPSsampling.xls
Interview_Tracking_Form.xls

14. Weights The Weights spreadsheet is used to
document the sample selection and
attach the weights to the dataset in Epi Info
Part of the spreadsheet is automated and parts need to be filled in by hand

15. Weights: Example
Information available from Rand Hhold spreadsheet Weighting Info
Automatically entered
Enter by hand by matching information from PSU and Clustering SSU
Information available from Clustering SSU spreadsheet Weighting Info

16. Attaching the Weights to Your Dataset
Once you have documented your weights using the
STEPSsampling.xls
Interviewtracking.xls
THEN …
You can use the generic analysis programs to automatically attach the weights to your dataset