two.level.normal.LR: Likelihood ratio calculation - normal

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

View source: R/two.level.normal.LR.r

Description

Takes a compitem object which represents some control item, and a compitem object which represents a recovered item, then uses information from a compcovar object, which represents the information from the population, to calculate a likelihood ratio as a measure of the evidence given by the observations for the same/different source propositions.

Usage

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two.level.normal.LR(control, recovered, background)

Arguments

control

a compitem object with the control item information

recovered

a compitem object with the recovered item information

background

a compcovar object with the populational information

Details

Does the likelihood ratio calculations for a two-level model assuming that the between item distribution is uni/multivariate normal.

Value

Returns an estimate of the likelihood ratio

Note

Do not even think about using this function without the proper compcovar and compitem objects - it will not work.

Author(s)

Agnieszka Martyna [email protected] and David Lucy [email protected] - http://www.maths.lancs.ac.uk/~lucy.

References

Aitken, C.G.G. & Lucy, D. (2004) Evaluation of trace evidence in the form of multivariate data. Applied Statistics: 53(1); 109-122.

See Also

compcovar
compitem
two.level.comparison.items
two.level.components
two.level.density.LR

Examples

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# load this library
library(comparison)

# load Greg Zadora's glass data
data(glass)

# make it into a data frame
dat <- as.data.frame(glass)

# calculate a compcovar object based upon dat
# using K, Ca and Fe - warning - could take time
# on slower machines
Z <- two.level.components(dat, c(7,8,9), 1)

# calculate a compitem object representing the control item
control <- two.level.comparison.items(dat[1:6,], c(7,8,9))

# calculate a compitem object representing the recovered item
# known to be from the same item (item 1)
recovered.1 <- two.level.comparison.items(dat[7:12,], c(7,8,9))

# calculate a compitem object representing the recovered item
# known to be from a different item (item 2)
recovered.2 <- two.level.comparison.items(dat[19:24,], c(7,8,9))


# calculate the likelihood ratio for a known
# same source comparison - should be 51.16539
lr.1 <- two.level.normal.LR(control, recovered.1, Z)

# calculate the likelihood ratio for a known
# different source comparison - should be 0.02901532
lr.2 <- two.level.normal.LR(control, recovered.2, Z)

comparison documentation built on May 29, 2017, 9:08 a.m.