An interviewer observed babies born with birth defects and babies born without birth defects in the years between 2010 to 2015. He selected twenty mothers of babies born with birth defects for questioning to form Group A. He also selected twenty mothers with healthy babies for questioning to form Group B. The goal of the research is to study the impact of environmental toxins on birth defects. He printed forty pamphlets with questions and gave one pamphlet to each mother to fill out. The questions are written to lead all mothers to write down their views on the health of their babies. After the study, the interviewer realized that mothers of babies born with birth defects searched their memories more thoroughly than mothers with healthy babies. Which is the most obvious bias in this study?
