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Inclusion probabilities: Stratified Random Sampling

Source: R/strata_rs.R
strata_rs_probabilities.Rd

Returns each unit's probability of being sampled under stratified random sampling. Units in different strata routinely have different probabilities, and a sample drawn that way is not self-weighting.

Usage

strata_rs_probabilities(
  strata = NULL,
  prob = NULL,
  prob_unit = NULL,
  n = NULL,
  n_unit = NULL,
  strata_n = NULL,
  strata_prob = NULL,
  check_inputs = TRUE
)

Arguments

strata

A vector of length N indicating which stratum each unit belongs to. Can be a character, factor, or numeric vector. (required)

prob

Use for a design in which either floor(N_stratum*prob) or ceiling(N_stratum*prob) units are sampled within each stratum. Which of the two is used is itself random: the ceiling is drawn with probability equal to the fractional part of N_stratum*prob and the floor otherwise, which makes each unit's probability of inclusion exactly prob. Must be a real number between 0 and 1 inclusive. (optional)

prob_unit

Must be of length N. tapply(prob_unit, strata, unique) will be passed to strata_prob, so it must be constant within each stratum. (optional)

n

Use for a design in which the scalar n gives the fixed number of units to sample in every stratum. This count does not vary across strata. (optional)

n_unit

Must be of length N. tapply(n_unit, strata, unique) will be passed to strata_n, so it must be constant within each stratum. (optional)

strata_n

Use for a design in which the numeric vector strata_n gives the number of units to sample within each stratum. Must be as long as the number of strata, in the same order as sort(unique(strata)). (optional)

strata_prob

Use for a design in which strata_prob gives the probability of being sampled within each stratum. Must be in the same order as sort(unique(strata)). Differs from prob in that the probability of being sampled can vary across strata. (optional)

check_inputs

Logical. Whether to verify before sampling that the arguments are internally consistent: that counts do not exceed the stratum sizes, that probabilities lie between 0 and 1, that stratum-level arguments have one entry per stratum, and so on. Defaults to TRUE. Set to FALSE to skip the checks when drawing many samples from arguments that have already been verified; declaring the design once with declare_rs() and drawing from it with draw_rs() does this for you. (optional)

Value

A numeric vector of length N giving each unit's probability of being included in the sample.

Details

These are the quantities inverse-probability weights are built from: weight each sampled unit by the reciprocal of its inclusion probability, which obtain_inclusion_probabilities() extracts for you.

See also

strata_rs()

Examples


strata <- rep(c("A", "B", "C"), times = c(50, 100, 200))

probs <- strata_rs_probabilities(strata = strata)
table(strata, probs)
#>       probs
#> strata 0.5
#>      A  50
#>      B 100
#>      C 200

probs <- strata_rs_probabilities(strata = strata, prob = 0.2)
table(strata, probs)
#>       probs
#> strata 0.2
#>      A  50
#>      B 100
#>      C 200

probs <- strata_rs_probabilities(strata = strata, strata_prob = c(0.1, 0.2, 0.3))
table(strata, probs)
#>       probs
#> strata 0.1 0.2 0.3
#>      A  50   0   0
#>      B   0 100   0
#>      C   0   0 200

probs <- strata_rs_probabilities(strata = strata, strata_n = c(10, 40, 70))
table(strata, probs)
#>       probs
#> strata 0.2 0.35 0.4
#>      A  50    0   0
#>      B   0    0 100
#>      C   0  200   0