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Bias is the difference between survey result and population value due to incorrect measurements being taken or measurements being taken on a non-representative sample
Bias results from:
- Incorrect measurements, resulting in measurement bias
- Selection of a nonrepresentative sample, resulting in sampling bias
Bias can be present in surveys:
- Even if sampling and analysis are done correctly
- Even if the survey is done with a very large sample size
In sum, if have lots of bias,
- You have not done the measurements correctly and/or
- You have sampled the wrong people.
Bias usually cannot usually be quantitatively measured or calculated.