Find where a p-value curve crosses alpha — tipping

For rows that carry a param value (from stress_tipping() or stress_curve()), interpolates linearly between adjacent parameter values to find where the p-value crosses alpha, separately for each family.

Usage

tipping_point(rows, alpha = NULL)

Arguments

rows: A stress_rows data frame or a stress_census.
alpha: Significance level; defaults to the rows' own alpha.

Value

A data frame with one row per family: family, n points, param_min, param_max, p_min, p_max, crossing (the interpolated parameter value, NA when the curve does not cross) and direction ("up" when p rises through alpha with increasing parameter, "down" otherwise).

Examples

small <- mmrm::fev_data[mmrm::fev_data$USUBJID %in% paste0("PT", 1:60), ]
spec <- stress_spec(small, "FEV1", "USUBJID", "AVISIT", "ARMCD", "PBO", covariates = ~ FEV1_BL)
shift_pt3 <- function(d, v) { k <- d$USUBJID == "PT3"; d$FEV1[k] <- d$FEV1[k] + v; d }
tipping_point(stress_curve(spec, values = c(-20, 0, 20), modify = shift_pt3))
#>                                family n param_min param_max     p_min     p_max
#> perturbation curve perturbation curve 3       -20        20 0.1819731 0.4093701
#>                    crossing direction
#> perturbation curve       NA      <NA>