Problem of bias is maximum with
Coho study
Case study
Case control study
Experimental study
Bias is any systemic error in the determination of the association between exposure and disease. The relative risk may increase or decrease as a result of the bias it reflects some type of no compatibility between the study and control groups. The possibility of bias must be considered when evaluating a possible cause and effect relationship. (refer pgno 73, park 23rd edition)
Epidemiology