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Weighting Your Data

Weighting Your Data. 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. What does weighting do?. It accounts for

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Weighting Your Data

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  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. There are 12 districts and 3 are randomly selected; probability of selection at district level =.25 Example

  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. Example 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 • Population weight = Proportion of population/Proportion of sample • Population weight = (Age-Sex of population / Total population) (Age-Sex of sample / Total Sample)

  11. Example 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

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