LT_probit {ecotox} | R Documentation |

Calculates lethal time (LT) and its fiducial confidence limits (CL) using a probit analysis according to Finney 1971, Wheeler et al. 2006, and Robertson et al. 2007.

```
LT_probit(
formula,
data,
p = NULL,
weights = NULL,
subset = NULL,
log_base = NULL,
log_x = TRUE,
het_sig = NULL,
conf_level = NULL,
conf_type = NULL,
long_output = TRUE
)
```

`formula` |
an object of class |

`data` |
an optional data frame, list or environment (or object coercible by as.data.frame to a data frame) containing the variables in the model. If not found in data, the variables are taken from environment(formula), typically the environment from which |

`p` |
Lethal time (LT) values for given p, example will return a LT50 value if p equals 50. If more than one LT value wanted specify by creating a vector. LT values can be calculated down to the 1e-16 of a percentage (e.g. LT99.99). However, the tibble produced can and will round to nearest whole number. |

`weights` |
vector of 'prior weights' to be used in the fitting process. Only needs to be supplied if you are taking the response / total for your response variable within the formula call of |

`subset` |
allows for the data to be subseted if desired. Default set to |

`log_base` |
default is |

`log_x` |
default is |

`het_sig` |
significance level from person's chi square goodness-of-fit test that is used to decide if a heterogeneity factor is used. |

`conf_level` |
Adjust confidence level as necessary or |

`conf_type` |
default is |

`long_output` |
default is |

Returns a tibble with predicted LT for given p level, lower CL (LCL), upper CL (UCL), LCL, Pearson's chi square goodness-of-fit test (pgof), slope, intercept, slope and intercept p values and standard error, and LT variance.

Finney, D.J., 1971. Probit Analysis, Cambridge University Press, Cambridge, England, ISBN: 052108041X

Wheeler, M.W., Park, R.M., and Bailey, A.J., 2006. Comparing median lethal concentration values using confidence interval overlap or ratio tests, Environ. Toxic. Chem. 25(5), 1441-1444.10.1897/05-320R.1

Robertson, J.L., Savin, N.E., Russell, R.M. and Preisler, H.K., 2007. Bioassays with arthropods. CRC press. ISBN: 9780849323317

```
head(lamprey_time)
results <- LT_probit((response / total) ~ log10(hour),
p = c(50, 99),
weights = total,
data = lamprey_time,
subset = c(month == "May"))
# view calculated LT50 and LT99 for seasonal
# toxicity of a piscicide, 3-trifluoromethyl-4-nitrophenol, to lamprey in 2011
results
# dose-response curve can be plotted using 'ggplot2'
```

[Package *ecotox* version 1.4.4 Index]