Derivatives for variance of average p and average p(0) variance

Used in call to DeltaMethod from prob.se to get first derivatives

Usage

prob.deriv(par, model, parfct, observer = NULL, fittedmodel = NULL)

par: detection function parameter values
model: ddf model object
parfct: function of detection probabilities; currently only average (over covariates) detection probability p integrated over distance or average (over covariates) detection probability at distance 0; p(0)
observer: 1,2,3 for primary, secondary, or duplicates for average p(0); passed to fct
fittedmodel: full fitted ddf model when trial.fi or io.fi is called from trial or io respectively

Vector of values from fct at specified parameter values

Need to add equations here as I do not think they exist in any of the texts. These should probably be checked with simulation.

Jeff Laake