Sampling bias
Topic: Economic Data: Census, NSS, Surveys and Statistical Tools · NCERT: Class 11, Ch 2 "Collection of Data"; Class 11, Ch 8 "Use of Statistical Tools"
Meaning
Sampling bias happens when the sampling plan cannot reach part of the target population. Those people have no chance of being selected, so the results lean towards the groups that can be reached. It is a non-sampling error. Making the sample bigger does not fix it, because the missing groups stay missing.
Example
A phone or online survey misses people who have no phone or internet connection. A survey frame based on Census 2011 misses settlements that came up after 2011.
Don't confuse with
- Non-response error: here people are selected but cannot be contacted or refuse to answer. In sampling bias, they could never have been selected.
- Sampling error: this is the chance gap between a sample estimate and the true value. It falls as the sample grows. Sampling bias does not.