A poor cohort study is characterized by a failure to:

• clearly define comparison groups and/or measure exposures and outcomes in the same (preferably blinded),
• objective way in both exposed and non-exposed individuals and/or identify or appropriately control known confounders and/or
• carry out a sufficiently long and complete follow-up of patients

A poor case-control study is characterized by a failure to:

• clearly define comparison groups and/or
• fail to measure exposures and outcomes in the same (preferably blinded)
• objective way in both cases and controls and/or
• fail to identify or appropriately control known confounders