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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.