convert_age_to_thresh {LTFHPlus}

Convert age to threshold

Description

convert_age_to_thresh computes the threshold from a person's age using either the logistic function or the truncated normal distribution

Usage

convert_age_to_thresh(
  age,
  dist = "logistic",
  pop_prev = 0.1,
  mid_point = 60,
  slope = 1/8,
  min_age = 10,
  max_age = 90,
  lower = stats::qnorm(0.05, lower.tail = FALSE),
  upper = Inf
)

Arguments

age

A non-negative number representing the individual's age.

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_age

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

max_age

Only necessary if dist = "normal". A positive number representing the individual's latest age. 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 age, convert_age_to_thresh can be used to first compute the cumulative incidence rate (cir), which is then used to compute the threshold using either the logistic function or the truncated normal distribution. Under the logistic function, the formula used to compute the threshold from an individual's age is given by

qnorm(pop\_ prev / (1 + exp((mid\_ point - age) * slope)), lower.tail = F)

, while it is given by

qnorm((1 - (age-min\_ age)/max\_ age) * (pnorm(upper) - pnorm(lower)) + pnorm(lower))

under the truncated normal distribution.

Value

If age is a positive number and all other necessary arguments are valid, then convert_age_to_thresh returns a number, which is equal to the threshold.

Examples

curve(sapply(age, convert_age_to_thresh), from = 10, to = 110, xname = "age")