- Simple Random Sampling
- Stratified Sampling – divide the population into non-overlapping subgroups called strata and choose SRS within each subgroup. Thus the variance within each subgroup is less than the overall population variance.
- Cluster Sampling
- Systematic Sampling – select the kth item – hidden patterns
- Convenience or Volunteer Sampling : select the first n points
- Convenience or Volunteer Sampling
- Selection Bias – predicting polls from twitter data.
- Measurement or Response Bias – the type of questions such that the people who answer it differ from the people who are not answering it.
- Non-response Bias – if the individuals responding differ systematically from the people who are not responding. For example : a mandatory survey in canada which was sent to 1/5th of the people was changed to optional and was sent to 1/3rd of the people. Since, the response was voluntary and not mandatory, new immigrants were much less likely to respond to this survey.