Problem of bias is maximum with
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)
Coho study
Case study
Case control study
Experimental study
Epidemiology