Collecting data is an important first step in statistical analysis. The goal of statistics is to make inferences about a population based on a sample. How we collect the data is important. If the sample is not representative of the whole population, we cannot make inferences about the population from that sample.
The following are a few frequently used methods for collecting data:
- Personal Interview
- People usually respond when asked by a person but their answers may be influenced by the interviewer.
- Telephone Interview
- Cost-effective but need to keep it short since respondents tend to be impatient.
- Self-Administered Questionnaires
- Cost-effective but the response rate is lower and the respondents may be a biased sample.
- Direct Observation
- For certain quantities of interest, one may be able to measure it from the sample.
- Web-Based Survey
- Can only target the population who uses the web.