this slide gives an account of sample survey method

1. What is a Survey ?
A Survey collects information
Is a Census from all the population
Is a Poll if for political information
Is a Sample Survey if from just a sample
of a population

2. Conditions for a Survey
• Answer the Objectives
• Be Unbiased, Accurate
• Be Generalizable
• Be Ethical
• Be Economical

3. Before a Survey
• Define the Questions to be answer.
• Define the Sampling strategy.
• Design and Test the Questionnaire.
• Train the field workers.
• Define the technique for
crossvalidation.
• Define the final Analysis.

4. During the Survey
- Verify and crossvalidate the Questionnaire
- Check Time table and Budget
After the Survey
- Crosscheck again all the data
- Perform the main analysis
- Perform any exploratory data analysis.

5. The Question
The first task is to clearly and
concisely define the Main
Question of interest as well as
the Target Population of the
study.

6. Sampling Unit
The individual
A family
A group, i.e. a class.
Sampling Frame
Existing listing
New listing

7. Define the Precision or Tolerated error
of the estimates : 1% , 5%.
Are there any Nuisance factor to be
accounted for, which ones are important?

8. Stratification
• Sample size proportional to strata size
• Equal sample sizes from all strata
• Sample size inversely proportional to
strata variability.

9. Multiple Steps Sampling
Big Units
2nd Units
Sampling
Units

10. Questionnaire
• Short and Concise
• Open Questions
• Multiple choice
• Yes/No

11. Internal Validity
How to check if the subject
answers truthfully?
- Ask the same question twice?
Marital status
Spouse age
- Check frequency versus known data

12. External validity
Are the appropriate questions asked?
Are the questions understandable by
all the subjects in the sample.

13. Study of Trends
Cohort
Panel
same same
same
same
new
new

14. Interviewers in Follow
Up Studies
• Preferably be the same.
• If not the training must be the same.
• They must be comparable.

15. Preparing for Validation
• Lists of valid responses for each
question.
• Define code for: Missing values.
• Not applicable.
• Do not know.
• Automatically set the ‘Not applicable’
based on some previous question.

16. Definition of the Analysis
• Specific Objective 1
- Test to answer specific objective 1.
• Specific Objective 2
- Test to answer specific objective 2.
• Secondary objectives
- Test to investigate secondary
objectives.
• Exploratory Data Analysis.

17. During the Survey
• Collect questionnaires daily.
• Check yesterday questionnaires for
missing or invalid answers.
• Re-interview invalid questionnaires

18. The Time Table
The often forgotten tasks.
• Is the number of answered
questionnaires according to the
predicted for this date?.
• Is more time needed to fill up the
required number of questionnaires?
• Are more interviewers needed to
complete the task in time?

19. The Interim View
• Crosstabulate the descriptor variables.
i.e. age, gender, occupation, etc.
• Are they similar to the known ( or
assumed) distribution in the population?
• Are we getting a representative or a
biased sample?.
• Do we need more advertising of the
study in some sectors of the population?

20. After the Survey
• Check for outliers in all variables,
both singly and in logical pairs.
• Are the distributions and
scattergrams plausible ?
• Decide whether to impute or to
eliminate the clear mistakes.

21. Statistical Analysis
Main Analysis
Description of the sample
Predefined Main Statistical analysis
Statistical significance of results
Exploratory Analysis
Describe test / procedure used
Report results

22. The Report
• List of Objectives.
• Objectives achieved.
• Sample size estimated.
• Response rate in the sample.
• Main Statistical Analysis.
• Results with significance or Confidence
Interval of estimators.
• Statistical Power of the tests performed.
• Results of the Exploratory Data Analysis

23. Conclusions
• What was achieved.
• Did the main Analysis agree with
predictions and if not why?
• Interpretation of the results of the main
Analysis.
• Were any new hypothesis generated by
the EDA.
• Interpretation of the findings by the
EDA.
• Ideas for new research.