convert_liability_to_aoo {LTFHPlus}

Convert liability to age of onset

Description

convert_liability_to_aoo computes the age of onset from an individual's true underlying liability using either the logistic function or the truncated normal distribution.

Usage

convert_liability_to_aoo(
  liability,
  dist = "logistic",
  pop_prev = 0.1,
  mid_point = 60,
  slope = 1/8,
  min_aoo = 10,
  max_aoo = 90,
  lower = stats::qnorm(0.05, lower.tail = FALSE),
  upper = Inf
)

Arguments

liability

A number representing the individual's true underlying liability.

dist

A string indicating which distribution to use. If dist = "logistic", the logistic function will be used to compute the age of onset. If dist = "normal", the truncated normal distribution will be used instead. Defaults to "logistic".

pop_prev

Only necessary if dist = "logistic". A positive number representing the overall population prevalence. Must be at most 1. Defaults to 0.1.

mid_point

Only necessary if dist = "logistic". A positive number representing the mid point logistic function. Defaults to 60.

slope

Only necessary if dist = "logistic". A number holding the rate of increase. Defaults to 1/8.

min_aoo

Only necessary if dist = "normal". A positive number representing the individual's earliest age of onset. Defaults to 10.

max_aoo

Only necessary if dist = "normal". A positive number representing the individual's latest age of onset. Must be greater than min_aoo. Defaults to 90.

lower

Only necessary if dist = "normal". A number representing the lower cutoff point for the truncated normal distribution. Defaults to 1.645 (stats::qnorm(0.05, lower.tail = FALSE)).

upper

Only necessary if dist = "normal". A number representing the upper cutoff point of the truncated normal distribution. Must be greater or equal to lower. Defaults to Inf.

Details

Given a person's cumulative incidence rate (cir), convert_liability_to_aoo can be used to compute the corresponding age. Under the logistic function, the age is given by

mid\_ point - log(pop\_ prev/cir - 1) * 1/slope

, while it is given by

(1 - truncated\_ normal\_ cdf(liability = liability, lower = lower , upper = upper)) * max\_ aoo + min\_ aoo

under the truncated normal distribution.

Value

If liability is a number and all other necessary arguments are valid, then convert_liability_to_aoo returns a positive number, which is equal to the age of onset.

Examples

curve(sapply(liability, convert_liability_to_aoo), from = 1.3, to = 3.5, xname = "liability") 
curve(sapply(liability, convert_liability_to_aoo, dist = "normal"),
 from = qnorm(0.05, lower.tail = FALSE), to = 3.5, xname = "liability")