Construct an initial guess for the Emax model parameters

Construct an initial guess for the Emax model parameters

Usage

emax_nls_init(structural_model, covariate_model, data)

Arguments

structural_model

A two-sided formula of the form response ~ exposure

covariate_model

A list of two-sided formulas, each of specifying a covariate model for a structural parameter

data

A data frame

Value

A data frame

Examples

# use a heuristic to construct sensible start values, and plausible
# upper and lower bounds within which the estimate is expected to fall 
emax_nls_init(
  structural_model = rsp_1 ~ exp_1, 
  covariate_model = list(E0 ~ cnt_a, Emax ~ 1, logEC50 ~ 1), 
  data = emax_df
)
#> # A tibble: 3 × 5
#>   parameter covariate start  lower upper
#>   <chr>     <chr>     <dbl>  <dbl> <dbl>
#> 1 E0        Intercept  9.73  0.528  18.9
#> 2 Emax      Intercept  7.74 -1.47   16.9
#> 3 logEC50   Intercept  8.69  6.63   10.8

# compare to the values estimated:
coef(emax_nls(
  structural_model = rsp_1 ~ exp_1, 
  covariate_model = list(E0 ~ cnt_a, Emax ~ 1, logEC50 ~ 1), 
  data = emax_df
))
#>          E0_cnt_a      E0_Intercept    Emax_Intercept logEC50_Intercept 
#>         0.4861467         5.0548075         9.9697250         8.2688405