Bias (Porta 2008)	Definition
Bias in the presentation of data	Error due to irregularities produced bi digit preference, incomplete data, poor techniques of measurement, technically poor laboratory procedures, or intentional attempts to mislead.
Selection bias	Distortions that result from procedures used to select subjects and from factors that influence participation in the study.
Reporting bias	Selective revealing or suppression of information.
Design bias	The difference between a true value and that obtained as a result of faulty design of a study.