Document Detail

Studying time to pregnancy by use of a retrospective design.
MedLine Citation:
PMID:  15972942     Owner:  NLM     Status:  MEDLINE    
Biologic fertility can be measured using time to pregnancy (TTP). Retrospective designs, although lacking detailed timed information about behavior and exposure, are useful since they have a well-defined target population, often have good response rates, and are simpler and less expensive to conduct than prospective studies. This paper reviews retrospective TTP studies from a methodological viewpoint and shows how methodological problems can be avoided or minimized by appropriate study design, conduct, and analysis. Sensitivity analyses using data from four European retrospective TTP studies are presented to explore the issues. Although the identified biases tend to have small impacts, the effects are not systematic across studies, and sensitivity analyses are recommended routinely. Planning bias can be checked by comparing propensity to report contraceptive failures in different exposure groups. Medical intervention bias can be avoided by censoring and inclusion of unsuccessful pregnancy attempts. Truncation bias can be a serious problem if unrecognized, but it is avoidable with appropriate study design and/or analysis. Behavior change bias can be minimized by assessing the covariates at the beginning of unprotected intercourse. More complete inference is possible if the study design covers the whole population, not just those who achieve a pregnancy.
Michael Joffe; Jane Key; Nicky Best; Niels Keiding; Thomas Scheike; Tina Kold Jensen
Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't; Review     Date:  2005-06-22
Journal Detail:
Title:  American journal of epidemiology     Volume:  162     ISSN:  0002-9262     ISO Abbreviation:  Am. J. Epidemiol.     Publication Date:  2005 Jul 
Date Detail:
Created Date:  2005-07-04     Completed Date:  2005-08-16     Revised Date:  2014-02-19    
Medline Journal Info:
Nlm Unique ID:  7910653     Medline TA:  Am J Epidemiol     Country:  United States    
Other Details:
Languages:  eng     Pagination:  115-24     Citation Subset:  IM    
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MeSH Terms
Bias (Epidemiology)
Cohort Studies
Cross-Sectional Studies
Infertility / epidemiology
Maternal Age
Pregnancy / statistics & numerical data*
Pregnancy, Unplanned
Research Design
Retrospective Studies
Smoking / adverse effects
Time Factors
Grant Support
G9900635//Medical Research Council

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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