Draw Poisson count data

Usage

draw_count(
  mean = apply_link(latent, link),
  N = length(mean),
  link = "identity",
  latent = NULL,
  quantile_y = NULL,
  dispersion = 0
)

Arguments

mean: Mean count (lambda). Scalar or per-unit vector, already the rate the draw uses. Supplying it with a non-identity link is an error naming latent, because mean = log(3) with link = "log" reads as a request to exponentiate and no range check can tell it apart from a rate of 1.099.
N: Number of draws. Defaults to length(mean).
link: "identity" (default) or "log", or a function applied to latent. "log" exponentiates latent to get the rate. Any other name is an error. fabricatr 1.x accepts no link here at all, answering "Count data does not accept link functions".
latent: Latent variable on the log scale, exponentiated by link = "log" to give the rate.
quantile_y: Optional quantile vector for correlate.
dispersion: Overdispersion, a single non-negative number. The default 0 is the Poisson, whose variance equals its mean. A positive value draws from the negative binomial with the same mean and variance mean + dispersion * mean^2. It is the reciprocal of the theta that MASS::glm.nb() reports, and the alpha of Stata's nbreg.

Value

An integer vector of non-negative counts, of length N.

Examples

fabricate(N = 5, rate = c(0, 1, 5, 10, 50),
          Y = draw_count(mean = rate))
#> # A tibble: 5 × 3
#>   ID     rate     Y
#>   <chr> <dbl> <int>
#> 1 1         0     0
#> 2 2         1     0
#> 3 3         5     8
#> 4 4        10    13
#> 5 5        50    53

# same mean, variance 3 + 0.5 * 3^2 = 7.5 rather than 3
y <- draw_count(mean = 3, N = 10000, dispersion = 0.5)
c(mean(y), var(y))
#> [1] 2.994100 7.457611