ssdtools (version 2.5.0)

ssd_hc: Hazard Concentrations for Species Sensitivity Distributions

Description

Calculates concentration(s) with bootstrap confidence intervals that protect specified proportion(s) of species for individual or model-averaged distributions using parametric or non-parametric bootstrapping.

Usage

ssd_hc(x, ...)
# S3 method for list
ssd_hc(x, percent, proportion = 0.05, ...)
# S3 method for fitdists
ssd_hc(
  x,
  percent = deprecated(),
  proportion = 0.05,
  ...,
  average = TRUE,
  ci = FALSE,
  level = 0.95,
  nboot = 1000,
  min_pboot = 0.95,
  multi_est = deprecated(),
  est_method = "multi",
  ci_method = "weighted_samples",
  parametric = TRUE,
  delta = 9.21,
  samples = FALSE,
  save_to = NULL,
  control = NULL
)
# S3 method for fitburrlioz
ssd_hc(
  x,
  percent,
  proportion = 0.05,
  ...,
  ci = FALSE,
  level = 0.95,
  nboot = 1000,
  min_pboot = 0.95,
  parametric = FALSE,
  samples = FALSE,
  save_to = NULL
)

Value

A tibble of corresponding hazard concentrations.

Arguments

x

The object.

...

Unused.

percent

A numeric vector of percent values to estimate hazard concentrations for. Deprecated for proportion = 0.05.

proportion

A numeric vector of proportion values to estimate hazard concentrations for.

average

A flag specifying whether to provide model averaged values as opposed to a value for each distribution.

ci

A flag specifying whether to estimate confidence intervals (by bootstrapping).

level

A number between 0 and 1 of the confidence level of the interval.

nboot

A count of the number of bootstrap samples to use to estimate the confidence limits. A value of 10,000 is recommended for official guidelines.

min_pboot

A number between 0 and 1 of the minimum proportion of bootstrap samples that must successfully fit (return a likelihood) to report the confidence intervals.

multi_est

A flag specifying whether to estimate directly from the model-averaged cumulative distribution function (multi_est = TRUE) or to take the arithmetic mean of the estimates from the individual cumulative distribution functions weighted by the AICc derived weights (multi_est = FALSE).

est_method

A string specifying whether to estimate directly from the model-averaged cumulative distribution function (est_method = 'multi') or to take the arithmetic mean of the estimates from the individual cumulative distribution functions weighted by the AICc derived weights (est_method = 'arithmetic') or or to use the geometric mean instead (est_method = 'geometric').

ci_method

A string specifying which method to use for estimating the standard error and confidence limits from the bootstrap samples. The default and recommended value is still ci_method = "weighted_samples" which takes bootstrap samples from each distribution proportional to its AICc based weights and calculates the confidence limits (and SE) from this single set. ci_method = "multi_fixed" and ci_method = "multi_free" generate the bootstrap samples using the model-averaged cumulative distribution function but differ in whether the model weights are fixed at the values for the original dataset or re-estimated for each bootstrap sample dataset. The value ci_method = "MACL" (was ci_method = "weighted_arithmetic"), which is only included for historical reasons, takes the weighted arithmetic mean of the confidence limits while ci_method = GMACL which takes the weighted geometric mean of the confidence limits was added for completeness but is also not recommended. Finally ci_method = "arithmetic_samples" and ci_method = "geometric_samples" take the weighted arithmetic or geometric mean of the values for each bootstrap iteration across all the distributions and then calculate the confidence limits (and SE) from the single set of samples.

parametric

A flag specifying whether to perform parametric bootstrapping as opposed to non-parametrically resampling the original data with replacement.

delta

A non-negative number specifying the maximum absolute AIC difference cutoff. Distributions with an absolute AIC difference greater than delta are excluded from the calculations.

samples

A flag specfying whether to include a numeric vector of the bootstrap samples as a list column in the output.

save_to

NULL or a string specifying a directory to save where the bootstrap datasets and parameter estimates (when successfully converged) to.

control

A list of control parameters passed to stats::optim().

Methods (by class)

• ssd_hc(list): Hazard Concentrations for Distributional Estimates

• ssd_hc(fitdists): Hazard Concentrations for fitdists Object

• ssd_hc(fitburrlioz): Hazard Concentrations for fitburrlioz Object

Details

Model-averaged estimates and/or confidence intervals (including standard error) can be calculated by treating the distributions as constituting a single mixture distribution versus 'taking the mean'. When calculating the model averaged estimates treating the distributions as constituting a single mixture distribution ensures that ssd_hc() is the inverse of ssd_hp().

Distributions with an absolute AIC difference greater than a delta of by default 7 have considerably less support (wt < 0.01) and are excluded prior to calculation of the hazard concentrations to reduce the run time.

References

Burnham, K.P., and Anderson, D.R. 2002. Model Selection and Multimodel Inference. Springer New York, New York, NY. doi:10.1007/b97636.

See Also

predict.fitdists() and ssd_hp().

Examples

ssd_hc(ssd_match_moments())

fits <- ssd_fit_dists(ssddata::ccme_boron)
ssd_hc(fits)

fit <- ssd_fit_burrlioz(ssddata::ccme_boron)
ssd_hc(fit)