strata.data: Stratification of Univariate Survey Population Using the Data

In stratifyR: Optimal Stratification of Univariate Populations

Stratification of Univariate Survey Population Using the Data

Description

This function takes in the univariate population data (argument data) and a fixed sample size (n) to compute the optimum stratum boundaries (OSB) for a given number of strata (L), optimum sample sizes (nh), etc. directly from the data. The main idea used is from Khan et al (2008) whereby the problem of stratification is formulated into a Mathematical Programming Problem (MPP) using the best-fit frequency distribution and its parameters estimated from the data. This MPP is then solved for the OSB using a Dynamic Programming (DP) solution procedure.

Usage

strata.data(data, h, n, cost = FALSE, ch = NULL,
            method = c("dp", "cobyla", "global", "exact"),
            n_starts = 20L, max_iter = 2000L, tol = 1e-09,
            verbose = FALSE)

Arguments

data	A vector of values of the survey variable y for which the OSB are determined.
h	A numeric: denotes the number of strata to be created.
n	A numeric: denotes a fixed total sample size.
cost	A logical: has default cost=FALSE. If it is a stratum-cost problem, cost=TRUE, with which, one must provide the Ch parameter.
ch	A numeric: denotes a vector of stratum costs. When cost=FALSE, it has a default of NULL.
method	Character. Optimisation method. "dp" (default) is the original Dynamic Programming solver, globally optimal on a 1,000-point grid for the fitted distribution. "exact" runs Dynamic Programming on the data and returns the partition with the smallest empirical Neyman cost over all partitions with at least two units per stratum; with more than 20,000 distinct cut points it searches 20,000 cut points spread evenly in rank (set options(stratifyR.exact_max_cand = ) to change this). "cobyla" is a fast multi-start search (COBYLA and BOBYQA) on the empirical objective, and "global" is a DIRECT-L global search followed by local refinement.
n_starts	Integer. Number of random restarts for the COBYLA solver. Default 20L. Used only by "cobyla".
max_iter	Integer. Maximum function evaluations per COBYLA start. Default 2000L.
tol	Numeric. Convergence tolerance for COBYLA. Default 1e-9.
verbose	Logical. Print per-start progress. Default FALSE.

Value

strata.data returns an object of class "strata" with the Optimum Strata Boundaries (OSB; the upper boundary of each stratum, the last being the largest data value), stratum weights (Wh), stratum variances (Vh), Optimum Sample Sizes (nh), stratum population sizes (Nh) and sampling fraction (fh).

Author(s)

Karuna Reddy <[e-mail]>
MGM Khan <[e-mail]>

See Also

strata.distr

Examples

data(sugarcane)
dp    <- strata.data(sugarcane$Production, h = 4, n = 500)
exact <- strata.data(sugarcane$Production, h = 4, n = 500, method = "exact")
c(dp = dp$WhShTot, exact = exact$WhShTot)

## Not run: 
data <- rweibull(1000, shape=2, scale = 1.5)
hist(data)
obj <- strata.data(data, h = 2, n=300)
summary(obj)
#-------------------------------------------------------------
data(anaemia)
Iron <- anaemia$Iron
res <- strata.data(Iron, h = 2, n=350)
summary(res)
#-------------------------------------------------------------
data(SHS) #Household Spending data from stratification package
weight <- SHS$WEIGHT
hist(weight); length(weight)
res <- strata.data(weight, h = 2, n=500)
summary(res)
#-------------------------------------------------------------
data(sugarcane)
Production <- sugarcane$Production
hist(Production)
res <- strata.data(Production, h = 2, n=1000)
summary(res)
#-------------------------------------------------------------
#The function be dynamically used to visualize the the strata boundaries,
#for 2 strata, over the density (or observations) of the "mag" variable
#from the quakes data (with purrr and ggplot2 packages loaded).
output <- quakes %>%
          pluck("mag") %>%
          strata.data(h = 2, n = 300)
quakes %>%
      ggplot(aes(x = mag)) +
      geom_density(fill = "blue", colour = "black", alpha = 0.3) +
      geom_vline(xintercept = output$OSB, linetype = "dotted", color = "red")
#-------------------------------------------------------------

## End(Not run)

stratifyR documentation built on Oct. 18, 2026, 1:07 a.m.