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.
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 = F),
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 = F)).
- 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.
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.
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.
