title: Regression dilution methods for meta-analysis: assessing long-term variability in plasma fibrinogen among 27,247 adults in 15 prospective studies.
abstract: BACKGROUND
  Within-person variability in measured values of a risk factor can bias its association with disease. The extent of this regression dilution bias for plasma fibrinogen was investigated using repeat measurement data collected at varying time intervals on 27 247 adults in 15 prospective studies.
  
  
  METHODS
  Regression dilution ratios (RDRs) were estimated from a linear regression of repeat measurements on baseline values in each study and for each time interval, and pooled allowing for within- and between-study heterogeneity. RDRs were estimated both without and with adjustment for confounders, and factors were investigated that might influence the RDRs.
  
  
  RESULTS
  The unadjusted overall RDR was 0.51 (95% CI: 0.47, 0.55), which decreased to 0.46 (95% CI: 0.42, 0.49) after adjustment for age, sex and measured values of other established vascular risk factors. The RDR did not vary materially by assay method, age, sex or smoking status, but decreased at higher levels of baseline fibrinogen.
  
  
  CONCLUSIONS
  It is appropriate to use an RDR of 0.5 to correct approximately for regression dilution bias in plasma fibrinogen values; however, this correction factor may produce somewhat conservative hazard ratios in adjusted analyses, at higher fibrinogen concentrations and in follow-up beyond a decade. More generally, the methods described in this report have widespread applicability to quantifying regression dilution bias in repeatability data from multiple prospective studies.
authors.forename: Angela M
authors.initials: AM
authors.lastname: Wood
authors.forename: Ian
authors.initials: I
authors.lastname: White
authors.forename: Simon G
authors.initials: SG
authors.lastname: Thompson
authors.forename: Sarah
authors.initials: S
authors.lastname: Lewington
authors.forename: John
authors.initials: J
authors.lastname: Danesh
mesh_terms: D000328:Adult; D000367:Age Factors; D015982:Bias; D002318:Cardiovascular Diseases / Q000097:blood* / Q000503:physiopathology; D005260:Female; D005340:Fibrinogen / Q000032:analysis*; D006801:Humans; D008297:Male; D015201:Meta-Analysis as Topic; D011446:Prospective Studies; D012044:Regression Analysis; D012307:Risk Factors; D012737:Sex Factors; D012907:Smoking; D013997:Time Factors
chemical_list: D005340:Fibrinogen