cpt_missing_person: Missing Person-Based Conditional Probability Table
In mispitools: Missing Person Identification Tools

cpt_missing_person

R Documentation

Missing Person-Based Conditional Probability Table

Description

Computes a conditional probability table (CPT) representing the probability of observing evidence given the hypothesis that the unidentified person IS the missing person. This table represents P(D|H1), accounting for potential observation errors in sex, age, and hair color.

The function incorporates error rates (epsilon values) that model the probability of misclassifying the true characteristics of the missing person during observation.

Usage

cpt_missing_person(
  MPs = "F",
  MPc = 1,
  eps = 0.05,
  epa = 0.05,
  epc = error_matrix_hair()
)

Arguments

`MPs`	Character. Missing person's biological sex: "F" for female, "M" for male. Default: "F".
`MPc`	Integer (1-5). Missing person's hair color category: 1=Black, 2=Brown, 3=Blonde, 4=Red, 5=Gray/White. Default: 1.
`eps`	Numeric (0-1). Error rate for sex observation. The probability of incorrectly recording the sex. Default: 0.05.
`epa`	Numeric (0-1). Error rate for age categorization. The probability of classifying a person in the wrong age group (T0 instead of T1). Default: 0.05.
`epc`	Matrix. Hair color error/confusion matrix, typically created with `error_matrix_hair`. Rows represent true colors, columns represent observed colors. Default: `error_matrix_hair()`.

Details

For a female MP (MPs = "F"), the joint probabilities are:

P(F-T1) = (1 - eps) * (1 - epa): Correctly observed sex and age
P(F-T0) = (1 - eps) * epa: Correct sex, wrong age group
P(M-T1) = eps * (1 - epa): Wrong sex, correct age
P(M-T0) = eps * epa: Wrong sex and age

The hair color probabilities come from the error matrix row corresponding to the MP's true hair color.

Value

A 4x5 numeric matrix representing conditional probabilities under H1. Rows correspond to observed sex-age group combinations:

F-T1: Observed as Female, age within range
F-T0: Observed as Female, age outside range
M-T1: Observed as Male, age within range
M-T0: Observed as Male, age outside range

Columns correspond to observed hair colors 1-5. Each cell contains P(Observed Sex, Observed Age, Observed Color | H1, MP characteristics).

Deprecation

Soft-deprecated in mispitools 2.0. The per-feature H1 CPT it builds as an outer product is generalised by nongenetic_feature plus the unified per-feature engine (one feature per trait, combined downstream). The legacy function still works for the 2.0 release-candidate cycle and will be removed afterwards.

References

Marsico FL, et al. (2023). "Likelihood ratios for non-genetic evidence in missing person cases." Forensic Science International: Genetics, 66, 102891. \Sexpr[results=rd]{tools:::Rd_expr_doi("10.1016/j.fsigen.2023.102891")}

Examples

# Default: Female MP with black hair
cpt_h1 <- cpt_missing_person()
print(cpt_h1)

# Male MP with brown hair, higher error rates
cpt_h1_male <- cpt_missing_person(
  MPs = "M",
  MPc = 2,
  eps = 0.10,
  epa = 0.10
)

# Compare H1 and H2 to compute LR
cpt_h2 <- cpt_population()
lr_matrix <- cpt_h1 / cpt_h2
print(log10(lr_matrix))

mispitools documentation built on Aug. 26, 2026, 1:08 a.m.