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Summary Statistics for Marginal K Distribution

Source: R/06_pmf_marginal.R
summary_K_marginal.Rd

Computes comprehensive summary statistics for the marginal distribution of \(K_J\) under a Gamma prior on \(\alpha\).

Usage

summary_K_marginal(
  J,
  a,
  b,
  logS,
  M = .QUAD_NODES_DEFAULT,
  probs = c(0.05, 0.25, 0.5, 0.75, 0.95)
)

Arguments

J

Integer; sample size (positive integer >= 1).

a

Numeric; shape parameter of Gamma prior (> 0).

b

Numeric; rate parameter of Gamma prior (> 0).

logS

Matrix; pre-computed log-Stirling matrix.

M

Integer; number of quadrature nodes (default: 80).

probs

Numeric vector; probability levels for quantiles (default: c(0.05, 0.25, 0.5, 0.75, 0.95)).

Value

A list with components:

J

Sample size

a

Gamma shape parameter

b

Gamma rate parameter

mean

Mean \(E[K_J \mid a, b]\)

var

Variance \(Var(K_J \mid a, b)\)

sd

Standard deviation

cv

Coefficient of variation (sd/mean)

mode

Mode (most likely value)

median

Median (50th percentile)

quantiles

Named integer vector of quantiles at probs

pmf

Full PMF vector

cdf

Full CDF vector

Details

This function provides a complete summary of the marginal distribution, combining PMF-based and CDF-based statistics. The mean and variance computed from the PMF should match exact_K_moments() within numerical tolerance.

The probs argument allows customization of which quantiles to report, making it flexible for different reporting needs.

See also

pmf_K_marginal, exact_K_moments

Examples

logS <- compute_log_stirling(50)
summary <- summary_K_marginal(50, 1.5, 0.5, logS)

# View main statistics
summary$mean
#> [1] 8.355487
summary$var
#> [1] 22.76895
summary$mode
#> [1] 6
summary$quantiles
#>  q5 q25 q50 q75 q95 
#>   2   5   8  11  17 

# Custom quantiles
summary2 <- summary_K_marginal(50, 1.5, 0.5, logS,
                               probs = c(0.025, 0.5, 0.975))
summary2$quantiles
#>  q2 q50 q98 
#>   1   8  19 

# Compare with exact moments
exact <- exact_K_moments(50, 1.5, 0.5)
c(summary$mean - exact$mean, summary$var - exact$var)
#> [1] -7.105427e-15 -4.263256e-14