Evaluates how uniformly cells are distributed across strata using multiple metrics including coefficient of variation (CV), min/max ratio, and Gini coefficient. Lower values indicate more uniform distribution.
Value
An object of class ss_coverage_efficiency (list) containing:
- cell_counts
Integer vector of cells per stratum
- n_strata
Number of strata
- total_cells
Total number of cells
- mean_cells
Mean cells per stratum
- sd_cells
Standard deviation of cells per stratum
- cv
Coefficient of variation (sd/mean)
- min_cells
Minimum cells in any stratum
- max_cells
Maximum cells in any stratum
- min_max_ratio
Ratio of min to max (1.0 = perfect equality)
- range_cells
Range (max - min)
- gini
Gini coefficient (0 = perfect equality, 1 = inequality)
- efficiency_score
Qualitative assessment: "Excellent", "Good", "Fair", or "Poor"
- is_equal_area
Whether equal-area algorithm was used
Details
The function computes several metrics to assess uniformity:
Coefficient of Variation (CV): Ratio of standard deviation to mean. Lower values indicate more uniform distribution. For equal-area stratification, expect CV < 0.05.
Min/Max Ratio: Ratio of smallest to largest stratum. Value of 1.0 indicates perfect equality. Values > 0.9 are excellent.
Gini Coefficient: Standard inequality measure from economics. 0 = perfect equality, 1 = maximal inequality. Lower values indicate better uniformity.
Efficiency Score:
Excellent: CV < 0.1 and min/max > 0.9
Good: CV < 0.2 and min/max > 0.75
Fair: CV < 0.35 and min/max > 0.5
Poor: Otherwise
Examples
if (FALSE) { # \dontrun{
library(sf)
# Create study area
poly <- st_polygon(list(rbind(
c(0, 0), c(100, 0), c(100, 50), c(0, 50), c(0, 0)
)))
study_area <- st_sf(geometry = st_sfc(poly))
# Create stratification
set.seed(42)
strata <- ss_stratify(study_area, n_strata = 20, n_try = 5)
# Assess coverage efficiency
efficiency <- ss_coverage_efficiency(strata)
print(efficiency)
# Compare regular vs equal-area
strata_equal <- ss_stratify(study_area, n_strata = 20,
equal_area = TRUE, n_try = 5)
eff_regular <- ss_coverage_efficiency(strata)
eff_equal <- ss_coverage_efficiency(strata_equal)
cat("Regular CV:", eff_regular$cv, "\n")
cat("Equal-area CV:", eff_equal$cv, "\n")
} # }