title: Investigating Respondents and Nonrespondents of a Postal Breast Cancer Questionnaire Survey Regarding Differences in Age, Medical Conditions, and Therapy.
abstract: BACKGROUND
  Collecting patient-reported data via postal questionnaires is a common and frequently used technique. Selection bias may occur through lost data from nonrespondents. This study investigated differences in characteristics between respondents and nonrespondents of a postal breast cancer survey.
  
  
  METHODS
  The investigation was based on a cross-sectional postal questionnaire survey for the mandatory annual routine (re-)certification of accredited breast centers in North Rhine-Westphalia in 2010. Out of 4,444 patients meeting the inclusion criteria who gave their consent to participate, 3,856 respondents sent back a questionnaire and 588 nonrespondents did not. Using logistic regression, differences between respondents and nonrespondents regarding information gathered through hospital staff concerning age, affected breast, UICC (Union for International Cancer Control) staging and grading, ASA (American Society of Anesthesiologists) classification, neoadjuvant chemotherapy, and type of surgery were assessed.
  
  
  RESULTS
  Very young and very old patients sent back their questionnaire significantly less frequently, as did patients who showed a later cancer stage and poorer general health and those who underwent mastectomy.
  
  
  CONCLUSIONS
  Differences exist between respondents and nonrespondents with regard to age, disease, and therapy characteristics that need to be considered for the interpretation and generalizability of survey results due to selection bias.
authors.affiliation: IMVR - Institute of Medical Sociology, Health Services Research and Rehabilitation Science at the Faculty of Human Sciences and the Faculty of Medicine of the University of Cologne, Cologne, Germany.
authors.forename: Anna L
authors.initials: AL
authors.lastname: Frobeen
authors.affiliation: IMVR - Institute of Medical Sociology, Health Services Research and Rehabilitation Science at the Faculty of Human Sciences and the Faculty of Medicine of the University of Cologne, Cologne, Germany.
authors.forename: Christoph
authors.initials: C
authors.lastname: Kowalski
authors.affiliation: IMSIE - Institute of Medical Statistics, Informatics and Epidemiology of the University of Cologne, Cologne, Germany.
authors.forename: Verena
authors.initials: V
authors.lastname: Weiß
authors.affiliation: IMVR - Institute of Medical Sociology, Health Services Research and Rehabilitation Science at the Faculty of Human Sciences and the Faculty of Medicine of the University of Cologne, Cologne, Germany.
authors.forename: Holger
authors.initials: H
authors.lastname: Pfaff
keywords: Bias; Breast cancer; Nonrespondent; Questionnaire survey