equivalence.xyplot: Constructs graphical regression-based tests of equivalence...

Description Usage Arguments Details Value Warning Acknowledgements Note Author(s) References See Also Examples

Description

Implements regression-based tests of equivalence within lattice graphics.

Usage

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 equivalence.xyplot(formula, alpha, b0.ii, b1.ii,
add.smooth=FALSE, b0.absolute=FALSE, ...)  

Arguments

formula

a formula describing the form of conditioning plot. See the manual entry for xyplot for more details.

alpha

the size of the test

b0.ii

the half-length of the region of similarity for the intercept, can be relative or absolute (see below).

b1.ii

the half-length of the region of similarity for the slope.

add.smooth

adds a loess smooth to the graph.

b0.absolute

is b0.ii in absolute or relative units?

...

extra arguments passed on to xyplot

Details

The graphic created by this function was proposed by Robinson et al. (2005) as a visual summary of the regression-based TOST. At first glance the graph will look messy; interpretation eases with practice. The following points should be noted.

The implementation in Robinson et al. (2005) required shifting so that the predictor has 0 mean. This hack has been removed here so that the basic graph object is a plot of the two variables being compared.

Value

Run for its side effect of producing a lattice plot object.

Warning

The accuracy of the output of this function is contingent on the usual regression assumptions, which are not checked here. Caveat emptor! Consider using equiv.boot() for a bootstrap-based solution. Transforming either variable will probably complicate the analysis considerably.

Acknowledgements

Feedback from Mohammad Al-Ahmadi has been very useful for this function.

Note

This version produces a regression-based TOST for each level of the conditioning factor. There may be an argument for pooling the test across these levels, in which case some prepanel computations will be helpful.

The TOST requires only estimates and standard errors from the data. Therefore the linear model used in the panel function can be replaced by any model that will produce suitable estimates. For example, in applying this function to hierarchical data we have had success using lme() instead.

I'm not entirely convinced that all these lines on one image are a good idea. It's straightforward to remove some, or change the colours. Recommendations for graphics that are visually cleaner are welcome.

Author(s)

Andrew Robinson A.Robinson@ms.unimelb.edu.au

References

Robinson, A.P., R.A. Duursma, and J.D. Marshall. 2005. A regression-based equivalence test for model validation: shifting the burden of proof. Tree Physiology 25, 903-913.

See Also

tost.stat, xyplot, equiv.boot

Examples

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data(pref.4PG)
equivalence.xyplot(pref.4PG$stemvolinc ~ pref.4PG$volinc4PG,
                   alpha=0.05, b0.ii=0.25, b1.ii=0.25, add.smooth=TRUE, 
                   xlab=expression(paste("4PG decadal volume growth (", m^3,
                       ha^-1, decade^-1, ")", sep="")), 
                   ylab=expression(paste("Measured decadal volume growth (",
                       m^3, ha^-1, decade^-1, ")", sep="")))

data(pref.LAI)
equivalence.xyplot(pref.LAI$lai.pa ~ pref.LAI$lai.bl,
                   alpha=0.05, b0.ii=0.25, b1.ii=0.25,
                   xlab=expression(paste("LAI Beer-Lambert (", m^2, m^-2, ")",
                       sep="")), 
                   ylab=expression(paste("LAI Ceptometer (", m^2, m^-2, ")",
                       sep=""))) 


data(ufc)
ufc.ht <- ufc[!is.na(ufc$Height),]
equivalence.xyplot(ufc.ht$Height.m ~ ufc.ht$Height.m.p,
                   alpha=0.05, b0.ii=0.1, b1.ii=0.2,
                   xlab="Predicted height (m)",
                   ylab="Measured height (m)")

equivalence.xyplot(ufc.ht$Height.m ~ ufc.ht$Height.m.p | ufc.ht$Species,
                   alpha=0.05, b0.ii=0.1, b1.ii=0.2,
                   xlab="Predicted height (m)",
                   ylab="Measured height (m)",
                   subset=ufc.ht$Species %in%
                        levels(ufc.ht$Species)[table(ufc.ht$Species)>5])

equivalence documentation built on May 1, 2019, 9:15 p.m.