BlandAltman: Bland-Altman plot to assess agreement between two continuous...

In biostatUZH: Misc Tools of the Department of Biostatistics, EBPI, University of Zurich

Description

Agreement between two continuous measurements is usually assessed by plotting the difference vs. the mean of the two measurements, the so-called Bland-Altman plot. Methods can be used interchangeably if all observations in the Bland-Altman lie between the mean +/- two standard deviations, provided that differences in this range were not clinically important. Note that the function automatically only uses pairwise complete observations.

Usage

BlandAltman(x, y, conf.level = 0.95, group = NA, labx = "", laby = "", 
    maintit = "", limy = NA, plot = TRUE)

Arguments

x	Measurements of first method.
y	Measurements of second method.
conf.level	Confidence level for confidence intervals around limitis of agreement.
group	Factor that enables different colors for points (e.g. to mark observations at different timepoints).
labx	Character string, label for x-axis.
laby	Character string, label for y-axis.
maintit	Main title of plot.
limy	2-d vector containing upper and lower limit for scaling of y-axis.
plot	If TRUE Bland-Altman plot is generated.

Value

A list containing the following elements:

difference.mean	Mean difference.
difference.sd	Standard deviation of differences.
difference.se	Standard error of mean differences.
upper.agreement.limit	Upper limit of agreement.
lower.agreement.limit	Lower limit of agreement.
agreement.limit.se	Standard error of limits of agreement.
t.value	t-quantile used for computation of limits of agreement.

Author(s)

Kaspar Rufibach
[e-mail]

References

Bland, J.M. and Altman, D.G. (1986). Statistical methods for assessing agreement between two methods of clinical measurement. Lancet, 1, 307–310.

Examples

n <- 50
meas1 <- rnorm(n, 20, 4)
meas2 <- meas1 + rnorm(n, 0.5, 1)
time <- sample(c(rep(1, n / 2), rep(2, n / 2)))

BlandAltman(x = meas1, y = meas2, conf.level = 0.95, group = NA, labx = 
    "mean of measurements", laby = "difference of measurements", 
    maintit = "Assess agreement between measurement 1 and measurement 2", 
    limy = NA)

BlandAltman(x = meas1, y = meas2, conf.level = 0.95, group = time, labx = 
    "mean of measurements", laby = "difference of measurements",
    maintit = "Assess agreement between measurement 1 and measurement 2", 
    limy = NA)

biostatUZH documentation built on May 2, 2019, 6:06 p.m.