Complete Random Sampling

complete_rs draws a sample of a fixed size: exactly n of N units are sampled on every draw. Fixing the sample size is what distinguishes it from simple random sampling, where the realized size varies.

Usage

complete_rs(
  N,
  n = NULL,
  n_unit = NULL,
  prob = NULL,
  prob_unit = NULL,
  check_inputs = TRUE
)

Arguments

N

The number of units in the sampling frame. Must be a positive integer. (required)

n

Use for a design in which exactly n units are sampled. (optional)

n_unit

unique(n_unit) will be passed to n; must be the same for all units and of length N. (optional)

prob

Use for a design in which either floor(N*prob) or ceiling(N*prob) units are sampled, chosen so that each unit's probability of inclusion is exactly prob. Must be a real number between 0 and 1 inclusive. (optional)

prob_unit

unique(prob_unit) will be passed to prob; must be the same for all units and of length N. Under complete random sampling the probability cannot vary by unit; use simple_rs() if it must. (optional)

check_inputs

Logical. Whether to verify before sampling that the arguments are internally consistent: that n does not exceed N, that probabilities lie between 0 and 1, that vectors are of length N, 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 indicating whether each unit is sampled (1) or not (0).

Details

Set the number of units to sample directly with n, or give a target probability with prob and let complete_rs work out the number. When N*prob is not a whole number, either floor(N*prob) or ceiling(N*prob) units are sampled: the ceiling is drawn with probability equal to the fractional part of N*prob and the floor otherwise, which makes each unit's probability of inclusion exactly prob. Specify N and not more than one of n or prob.

If only N is specified, half the units are sampled. When N is odd, either floor(N/2) or ceiling(N/2) units are sampled.

See also

simple_rs(), strata_rs(), cluster_rs(), complete_ra(), complete_rs_probabilities()

Examples

S <- complete_rs(N = 100)
table(S)
#> S
#>  0  1 
#> 50 50 

S <- complete_rs(N = 100, n = 50)
table(S)
#> S
#>  0  1 
#> 50 50 

S <- complete_rs(N = 100, n_unit = rep(30, 100))
table(S)
#> S
#>  0  1 
#> 70 30 

S <- complete_rs(N = 100, prob = 0.111)
table(S)
#> S
#>  0  1 
#> 89 11 

S <- complete_rs(N = 100, prob_unit = rep(0.1, 100))
table(S)
#> S
#>  0  1 
#> 90 10 

# If N = n, every unit is sampled with probability 1
complete_rs(N = 2, n = 2)
#> [1] 1 1

# The single-unit case works the same way: n = 1 out of N = 1 is sampled
# with probability 1. Up through randomizr 0.12.0 this case was instead
# treated as a coin flip, so the unit was sampled only half of the time.
# The change is noted here because it silently alters the inclusion
# probabilities in code written against those versions.
complete_rs(N = 1, n = 1)
#> [1] 1