title: A simulation study of nonparametric total deviation index as a measure of agreement based on quantile regression.
abstract: Total deviation index (TDI) captures a prespecified quantile of the absolute deviation of paired observations from raters, observers, methods, assays, instruments, etc. We compare the performance of TDI using nonparametric quantile regression to the TDI assuming normality (Lin, 2000). This simulation study considers three distributions: normal, Poisson, and uniform at quantile levels of 0.8 and 0.9 for cases with and without contamination. Study endpoints include the bias of TDI estimates (compared with their respective theoretical values), standard error of TDI estimates (compared with their true simulated standard errors), and test size (compared with 0.05), and power. Nonparametric TDI using quantile regression, although it slightly underestimates and delivers slightly less power for data without contamination, works satisfactorily under all simulated cases even for moderate (say, ≥40) sample sizes. The performance of the TDI based on a quantile of 0.8 is in general superior to that of 0.9. The performances of nonparametric and parametric TDI methods are compared with a real data example. Nonparametric TDI can be very useful when the underlying distribution on the difference is not normal, especially when it has a heavy tail.
authors.affiliation: a JBS Consulting Services Inc. , Carlsbad , California , USA.|b Department of Mathematics , Statistics and Computer Science, University of Illinois , Chicago , Illinois , USA.
authors.forename: Lawrence
authors.initials: L
authors.lastname: Lin
authors.affiliation: c Division of HIV/AIDS Prevention-Surveillance and Epidemiology , Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention, Centers for Disease Control and Prevention , Atlanta , Georgia , USA.
authors.forename: Yi
authors.initials: Y
authors.lastname: Pan
authors.affiliation: b Department of Mathematics , Statistics and Computer Science, University of Illinois , Chicago , Illinois , USA.
authors.forename: A S
authors.initials: AS
authors.lastname: Hedayat
authors.affiliation: d Department of Biostatistics and Bioinformatics , Duke Clinical Research Institute, Duke University , Durham , North Carolina , USA.
authors.forename: Huiman X
authors.initials: HX
authors.lastname: Barnhart
authors.affiliation: e Department of Biostatistics and Bioinformatics , Rollins School of Public Health, Emory University , Atlanta , Georgia , USA.
authors.forename: Michael
authors.initials: M
authors.lastname: Haber
mesh_terms: D003198:Computer Simulation; D006801:Humans; D012044:Regression Analysis; D018709:Statistics, Nonparametric
keywords: Agreement; nonparametric; quantile regression; total deviation index (TDI)