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Research
Economic Impact of Lyme Disease
Xinzhi Zhang,*
Martin I. Meltzer,* César A. Peña,†1 Annette
B. Hopkins,† Lane Wroth,‡ and Alan D. Fix†
*Centers for Disease Control and Prevention, Atlanta, Georgia, USA; †University
of Maryland, Baltimore, Maryland, USA; and ‡Care First-Easton Branch (previously
Delmarva Health Plan), Easton, Maryland, USA
Appendix 3. Multivariate Regression
Model
We used a multivariate linear regression model to estimate the relative
impact of a number of factors on the direct medical costs of Lyme disease
(LD).
Yi = Xi β + εi
where Yi, the dependent variable, is the total direct
medical costs for patient i and Xi is a vector of covariates.
εi is a mean-zero random error. Baseline costs came
from the intercept term, which refers to a female patient who had tick
bite only (without erythema migrans symptoms) diagnosed in 1997 during
an office visit. Such a patient had no hospital or emergency room stay,
no serologic tests, no consultation from other physicians, no antimicrobial
drug therapy, and no other procedures outside physician office and hospital/emergency
room. Additional direct medical costs were added or subtracted to the
baseline costs for each independent variable of interest if statistically
significant. Therefore, total direct medical costs per LD patient = baseline
costs + cost difference of different patient diagnosis group (early stage
LD, late stage LD, suspected LD, other LD relevant complain vs. tick bite
) + costs of serologic test + costs of other procedure outside physician
office and hospital/emergency room + costs of hospital and/or emergency
room stay + costs of consultation from other physicians + costs of therapy
+ miscellaneous costs + cost difference with or without erythema migrans
+ cost difference of gender + cost difference of each additional year
of age + cost difference of cohort year, if statistically significant.
1Current affiliation: Maryland Department
of Health and Mental Hygiene, Baltimore, Maryland, USA
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