This type of bias refers to a research participant’s difficulty in accurately remembering information they are asked for in a retrospective study. For example, in a retrospective study on alcohol exposure during pregnancy, women may be asked about their alcohol intake during pregnancy much later, such as months after they have given birth. By then, they may not be able to recall their alcohol consumption as accurately as if they had been asked in a prospective study going on during their pregnancy.
Another way recall bias might interfere in a case control study is that cases — those with a condition — may be more likely to remember their exposure to a particular substance or experience than those in the control group who do not have the condition being studied. Someone with asthma, for example, may more easily recall the last time they sat in stopped highway traffic than someone without asthma and therefore without as much reason to remember a circumstance that might worsen a condition they don’t have.