title: Maternal Recall Error in Retrospectively Reported Time-to-Pregnancy: an Assessment and Bias Analysis.
abstract: BACKGROUND
  Epidemiologic studies of fecundability often use retrospectively measured time-to-pregnancy (TTP), thereby introducing potential for recall error. Little is known about how recall error affects the bias and precision of the fecundability odds ratio (FOR) in such studies.
  
  
  METHODS
  Using data from the Danish Snart-Gravid Study (2007-12), we quantified error for TTP recalled in the first trimester of pregnancy relative to prospectively measured TTP among 421 women who enrolled at the start of their pregnancy attempt and became pregnant within 12 months. We defined recall error as retrospectively measured TTP minus prospectively measured TTP. Using linear regression, we assessed mean differences in recall error by maternal characteristics. We evaluated the resulting bias in the FOR and 95% confidence interval (CI) using simulation analyses that compared corrected and uncorrected retrospectively measured TTP values.
  
  
  RESULTS
  Recall error (mean = -0.11 months, 95% CI -0.25, 0.04) was not appreciably associated with maternal age, gravidity, or recent oral contraceptive use. Women with TTP > 2 months were more likely to underestimate their TTP than women with TTP ≤ 2 months (unadjusted mean difference in error: -0.40 months, 95% CI -0.71, -0.09). FORs of recent oral contraceptive use calculated from prospectively measured, retrospectively measured, and corrected TTPs were 0.82 (95% CI 0.67, 0.99), 0.74 (95% CI 0.61, 0.90), and 0.77 (95% CI 0.62, 0.96), respectively.
  
  
  CONCLUSIONS
  Recall error was small on average among pregnancy planners who became pregnant within 12 months. Recall error biased the FOR of recent oral contraceptive use away from the null by 10%. Quantitative bias analysis of the FOR can help researchers quantify the bias from recall error.
authors.affiliation: Department of Epidemiology, Boston University School of Public Health, Boston, MA, USA.|Epidemiology Branch, Division of Intramural Population Health Research, Eunice Kennedy Shriver National Institute of Child Health and Human Development, North Bethesda, MD, USA.
authors.forename: Rose G
authors.initials: RG
authors.lastname: Radin
authors.affiliation: Department of Epidemiology, Boston University School of Public Health, Boston, MA, USA.|RTI Health Solutions, Research Triangle Park, NC.
authors.forename: Kenneth J
authors.initials: KJ
authors.lastname: Rothman
authors.affiliation: Department of Epidemiology, Boston University School of Public Health, Boston, MA, USA.
authors.forename: Elizabeth E
authors.initials: EE
authors.lastname: Hatch
authors.affiliation: Department of Clinical Epidemiology, Aarhus University Hospital, Aarhus, Denmark.
authors.forename: Ellen M
authors.initials: EM
authors.lastname: Mikkelsen
authors.affiliation: Department of Epidemiology, Boston University School of Public Health, Boston, MA, USA.|Department of Clinical Epidemiology, Aarhus University Hospital, Aarhus, Denmark.
authors.forename: Henrik T
authors.initials: HT
authors.lastname: Sorensen
authors.affiliation: Department of Clinical Epidemiology, Aarhus University Hospital, Aarhus, Denmark.
authors.forename: Anders H
authors.initials: AH
authors.lastname: Riis
authors.affiliation: Department of Epidemiology, Boston University School of Public Health, Boston, MA, USA.|Center for Global Health and Development, Boston University, Boston, MA, USA.
authors.forename: Matthew P
authors.initials: MP
authors.lastname: Fox
authors.affiliation: Department of Epidemiology, Boston University School of Public Health, Boston, MA, USA.|Slone Epidemiology Center, Boston University, Boston, MA, USA.
authors.forename: Lauren A
authors.initials: LA
authors.lastname: Wise
mesh_terms: D000328:Adult; D015982:Bias; D005260:Female; D005298:Fertility / Q000502:physiology; D006801:Humans; D016014:Linear Models; D011939:Mental Recall; D016017:Odds Ratio; D011247:Pregnancy; D015203:Reproducibility of Results; D012189:Retrospective Studies; D011795:Surveys and Questionnaires; D061685:Time-to-Pregnancy
keywords: Bias (Epidemiology); Cohort Studies; Fertility Determinants