logistic function

Analysis: Logistic regression

Logistic regression is a very popular analysis in agrarian sciences, such as in fruit growth curves, seed germination, etc...The logistic function performs the analysis using 3 or 4 parameters of the logistic model, being imported from the LL function .3 or LL.4 of the drc package (Ritz & Ritz, 2016).

logistic(
  trat,
  resp,
  npar = "LL.3",
  error = "SE",
  ylab = "Dependent",
  xlab = expression("Independent"),
  theme = theme_classic(),
  legend.position = "top",
  r2 = "all",
  width.bar = NA,
  scale = "none",
  textsize = 12,
  font.family = "sans"
)

Arguments

• trat: Numerical or complex vector with treatments
• resp: Numerical vector containing the response of the experiment.
• npar: Number of model parameters
• error: Error bar (It can be SE - default, SD or FALSE)
• ylab: Variable response name (Accepts the expression() function)
• xlab: Treatments name (Accepts the expression() function)
• theme: ggplot2 theme (default is theme_bw())
• legend.position: Legend position (default is c(0.3,0.8))
• r2: Coefficient of determination of the mean or all values (default is all)
• width.bar: Bar width
• scale: Sets x scale (default is none, can be "log")
• textsize: Font size
• font.family: Font family (default is sans)

Returns

The function allows the automatic graph and equation construction of the logistic model, provides important statistics, such as the Akaike (AIC) and Bayesian (BIC) inference criteria, coefficient of determination (r2), square root of the mean error ( RMSE).

Details

The three-parameter log-logistic function with lower limit 0 is

The four-parameter log-logistic function is given by the expression

The function is symmetric about the inflection point (e).

Examples

data("emerg")
with(emerg, logistic(time, resp,xlab="Time (days)",ylab="Emergence (%)"))
with(emerg, logistic(time, resp,npar="LL.4",xlab="Time (days)",ylab="Emergence (%)"))

References

Seber, G. A. F. and Wild, C. J (1989) Nonlinear Regression, New York: Wiley and Sons (p. 330).

Ritz, C.; Strebig, J.C.; Ritz, M.C. Package ‘drc’. Creative Commons: Mountain View, CA, USA, 2016.

Author(s)

Model imported from the drc package (Ritz et al., 2016)

Gabriel Danilo Shimizu

Leandro Simoes Azeredo Goncalves