Description Usage Arguments Details Value Author(s) References Examples

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

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.

1 | ```
two.level.normal.LR(control, recovered, background)
``` |

`control` |
a |

`recovered` |
a |

`background` |
a |

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

an estimate of the likelihood ratio

Agnieszka Martyna and David Lucy

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

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 | ```
# load Greg Zadora's glass data
data(glass)
# calculate a compcovar object based upon glass
# using K, Ca and Fe - warning - could take time
# on slower machines
Z <- two.level.components(glass, c(7,8,9), 1)
# calculate a compitem object representing the control item
control <- two.level.comparison.items(glass[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(glass[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(glass[19:24,], c(7,8,9))
# calculate the likelihood ratio for a known
# same source comparison - should be 51.16539
# This value is 51.14243 in this version and the last version David wrote (1.0-4)
lr.1 <- two.level.normal.LR(control, recovered.1, Z)
lr.1
# calculate the likelihood ratio for a known
# different source comparison - should be 0.02901532
# This vsalue is 0.02899908 in this version and the last version David wrote (1.0-4)
lr.2 <- two.level.normal.LR(control, recovered.2, Z)
lr.2
``` |

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