What is a Survey ?

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
Sampling Units
2nd Units
Big 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
same
same
same
Panel
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 TableThe 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.