Global Moran's I (spatial autocorrelation)

Do neighbouring countries have similar values? Global Moran's I on the country spine, using the country_borders() land-border adjacency as the spatial weights (row-standardised), with a permutation pseudo-p-value. No spdep required: at ~200 countries the dense arithmetic is trivial, and reusing the package's own adjacency keeps the weights consistent with the maps. Countries with no land border in the data (islands) carry no weight and are excluded.

Usage

morans_i(data, value, scale = "small", n_perm = 999)

Arguments

data

A country-level data frame with iso3c (map-ready frames are reduced to one row per country).

value

The value column (unquoted).

scale

Natural Earth resolution for the adjacency (see country_borders()).

n_perm

Number of permutations for the pseudo-p-value (default 999; use 0 to skip the test).

Value

A one-row tibble: i (observed Moran's I), expected (\(-1/(n-1)\) under no autocorrelation), n (countries used), n_links (border pairs among them) and p_value (one-sided, \(P(I_{perm} \ge I_{obs})\); positive autocorrelation is the standard alternative). Set a seed beforehand for a reproducible p_value.

Examples

if (FALSE) { # \dontrun{
snap <- countryatlas::world_snapshot$countries
set.seed(42)
morans_i(snap, gdp_per_capita)   # GDP clusters strongly in space
} # }