title: Reasons for non-response in observational pharmacogenetic research.
abstract: OBJECTIVE
  In epidemiological studies, non-response may introduce bias and limit generalizability. In genetic pharmacoepidemiological research, collection of DNA might be a major reason for non-response. We determined reasons for non-response and compared characteristics of non-responders and responders in a pharmacogenetic case-control study.
  
  
  METHODS
  Myocardial infarction (MI) cases and controls, who were antihypertensive drug users, were recruited through community pharmacies that participate in the Pharmaco-Morbidity-Record-Linkage-System (PHARMO). The PHARMO database comprises drug dispensing histories of about 2 000 000 subjects from a representative sample of Dutch community pharmacies linked to the national registry of hospital discharges. Independent samples t-test and ANOVA-statistics were used to analyse the differences in continuous variables between responders and non-responders. chi2 statistics and logistic regression were used to compare categorical variables.
  
  
  RESULTS
  We approached 1871 cases and 14 102 controls of whom 794 MI cases (42.4%) and 4997 controls (35.4%) responded. We could not approach 2194 patients of whom 63.1% had died and 31.2% moved to another pharmacy. Main reasons for non-response were health problems or hospital stays (16.2%, OR 1.47; 95%CI: 1.00-2.16). Other reasons were old age or dementia (16.9%, OR 1.82; 95%CI: 1.24-2.65). Only a small percentage (1.1%, OR 1.43; 95%CI: 0.41-5.03) mentioned DNA sampling as a reason. About 30% of the non-responders did not give a reason. Women were statistically significantly (p < 0.0005) less willing to participate than men (38.8% versus 31.3%). An association with age was also found (mean age 64.6 versus 66.5 yrs) (p < 0.0005).
  
  
  CONCLUSIONS
  In a pharmacogenetic case-control study fear for genetic screening was not a major reported reason for non-response. Females were less willing to participate than males.
authors.affiliation: Department of Pharmacoepidemiology and Pharmacotherapy, Utrecht Institute for Pharmaceutical Sciences (UIPS), University of Utrecht, the Netherlands.
authors.forename: Diane B M A
authors.initials: DB
authors.lastname: van Wieren-de Wijer
authors.forename: Anke-Hilse
authors.initials: AH
authors.lastname: Maitland-van der Zee
authors.forename: Anthonius
authors.initials: A
authors.lastname: de Boer
authors.forename: Abraham A
authors.initials: AA
authors.lastname: Kroon
authors.forename: Peter W
authors.initials: PW
authors.lastname: de Leeuw
authors.forename: Paul
authors.initials: P
authors.lastname: Schiffers
authors.forename: Rob G J H
authors.initials: RG
authors.lastname: Janssen
authors.forename: Bruce M
authors.initials: BM
authors.lastname: Psaty
authors.forename: Cornelia M
authors.initials: CM
authors.lastname: van Duijn
authors.forename: Bruno H Ch
authors.initials: BH
authors.lastname: Stricker
authors.forename: Olaf H
authors.initials: OH
authors.lastname: Klungel
mesh_terms: D000328:Adult; D000368:Aged; D000959:Antihypertensive Agents / Q000627:therapeutic use*; D016022:Case-Control Studies; D016009:Chi-Square Distribution; D015709:Correspondence as Topic; D005239:Fear; D005240:Feasibility Studies; D005260:Female; D030661:Genetic Privacy; D005820:Genetic Testing; D007722:Health Knowledge, Attitudes, Practice; D006801:Humans; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D009203:Myocardial Infarction / Q000188:drug therapy* / Q000453:epidemiology; D009426:Netherlands / Q000453:epidemiology; D016017:Odds Ratio; D018579:Patient Selection; D010597:Pharmacogenetics / Q000379:methods; D012042:Registries; D035842:Research Subjects / Q000523:psychology*; D018570:Risk Assessment; D012307:Risk Factors; D011795:Surveys and Questionnaires; D013689:Telephone
chemical_list: D000959:Antihypertensive Agents