Participation bias assessment in a community-based study of myocardial infarction, 2002-2005.
OBJECTIVE
To compare the characteristics and survival of participants and nonparticipants in a community-based study of myocardial infarction (MI).


METHODS
Residents of Olmsted County, MN, who presented with elevated cardiac troponin T levels from September 1, 2002, through December 31, 2005, were prospectively enrolled and classified with standardized criteria for MI. With specific Institutional Review Board approval, the medical records of patients with MI who did not provide consent but who had given general research authorization were reviewed, as was done for their consenting peers.


RESULTS
During the study period, 2277 individuals with elevated cardiac troponin T levels were approached, of whom 1863 (82 percent) consented to participate. Among the 414 nonparticipants, 375 (91 percent) had general research authorization. Of the 558 with general research authorization who met the criteria for incident (ie, first-ever) MI, 67 (12 percent) refused to participate. These participants tended to be older (mean plus or minus SD age, 71 plus or minus 14 vs 67 plus or minus 15 years; P equals .04), were more likely to be of races other than white (9 percent vs 2 percent; P equals .01), and had more comorbidities, including peripheral vascular disease (P equals .02), chronic pulmonary disease (P equals .06), heart failure (P equals .07), and impaired creatinine clearance (P equals .02). No significant differences were detected in cardiovascular risk factors or MI characteristics. During a median follow-up of 517 days, nonparticipants experienced increased mortality rates compared with participants (hazard ratio, 1.97; 95 percent confidence interval, 1.21 to 3.20), which was largely attributable to their older age and excess comorbidities (adjusted hazard ratio, 1.43; 95 percent confidence interval, 0.86 to 2.35).


CONCLUSIONS
In this community-based study of MI, nonparticipants experienced worse survival rates than participants largely because of differences in demographic and clinical characteristics. These differences should be kept in mind when interpreting study results, particularly if participation is low.
Division of Cardiovascular Diseases, Mayo Clinic, 200 First Street SW, Rochester, MN 55905, USA.
Yariv
Y
Gerber
Steven J
SJ
Jacobsen
Jill M
JM
Killian
Susan A
SA
Weston
Veronique L
VL
Roger
D000367:Age Factors; D000368:Aged; D015982:Bias; D002303:Cardiac Output, Low / Q000453:epidemiology; D002908:Chronic Disease; D003404:Creatinine / Q000652:urine; D005500:Follow-Up Studies; D006801:Humans; D007258:Informed Consent; D008171:Lung Diseases / Q000453:epidemiology; D008910:Minnesota / Q000453:epidemiology; D009203:Myocardial Infarction / Q000453:epidemiology*; D010358:Patient Participation / Q000706:statistics & numerical data*; D016491:Peripheral Vascular Diseases / Q000453:epidemiology; D011159:Population Surveillance; D011446:Prospective Studies; D044469:Racial Groups; D045808:Refusal to Participate / Q000706:statistics & numerical data*; D012307:Risk Factors; D015996:Survival Rate; D020107:Troponin T / Q000097:blood
D020107:Troponin T; D003404:Creatinine