You are conducting a hypothetical retrospective study on use of plastics and prevalence of current medical problems in UCI students. You hypothesize that participants who used more plastic cups in high school will exhibit more medical problems today. You ask all PH1 students to recall how many times they drank out of plastic cups in high school. Your participants struggle to recall this information and end up guessing how often they used plastic drinking containers in high school. Your study design will be negatively impacted by: (select one)