Confounding

  • unaccounted confounding variable - treatment and the control group differ in some third variable which influences the response that is being studied
    • e.g. a hospital may select healthier subjects for surgery

Data Collection Bias

When we conduct a experiment or survey, there are many possible sources of possible bias. For example:

  • sampling bias - sample is collected in such a way that some members of the intended population have a lower or higher sampling probability than others
  • observer bias - when the participants or investigators are aware of the identity of the 2 groups, and so we can get bias in either the responses or evaluations

Bias of an Estimator

The bias of an estimator is the difference between an estimator’s expected value and the true value of the parameter being estimated.

Interpretation

Probability Biases