To minimize<unk> , some clinical trials have adopted a "wash out period", i.e., a substantial time period that must elapse between the subject's first observation and their subsequent observation of the same event. Use of hospital records rather than patient experience can also help to avoid<unk> . Standardising sampling methods can help to avoid needing<unk>  information in the first place. Often,<unk>  is difficult to avoid, and many studies change experiment design to avoid<unk> ing information.
Recall bias
Publication bias
Information bias 
Funding bias
Length time bias
Lead time bias
Age bias 
Restraint bias