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authorNaeem Model <me@nmode.ca>2024-01-10 14:50:22 +0000
committerNaeem Model <me@nmode.ca>2024-01-10 14:50:22 +0000
commite1c61de5a0e693e2f24a1c4a10336e2a1c4563cb (patch)
tree92b4c42ef15fbda45dde6f5ec306d4bfe344a798 /R/ID.R
parent95b5ad6ce6ec5f76094b1e7176acfd44ffeef4e9 (diff)
Rename ID and IDEA
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-#' ID method
-#'
-#' This function implements a least squares estimation method of R0 due to
-#' Fisman et al. (PloS One, 2013). See details for implementation notes.
-#'
-#' The method is based on a straightforward incidence decay model. The estimate
-#' of R0 is the value which minimizes the sum of squares between observed case
-#' counts and cases counts 'expected' under the model.
-#'
-#' This method is based on an approximation of the SIR model, which is most
-#' valid at the beginning of an epidemic. The method assumes that the mean of
-#' the serial distribution (sometimes called the serial interval) is known. The
-#' final estimate can be quite sensitive to this value, so sensitivity testing
-#' is strongly recommended. Users should be careful about units of time (e.g.,
-#' are counts observed daily or weekly?) when implementing.
-#'
-#' @param NT Vector of case counts.
-#' @param mu Mean of the serial distribution. This needs to match case counts
-#' in time units. For example, if case counts are weekly and the
-#' serial distribution has a mean of seven days, then \code{mu} should
-#' be set to one. If case counts are daily and the serial distribution
-#' has a mean of seven days, then \code{mu} should be set to seven.
-#'
-#' @return \code{ID} returns a single value, the estimate of R0.
-#'
-#' @examples
-#' # Weekly data:
-#' NT <- c(1, 4, 10, 5, 3, 4, 19, 3, 3, 14, 4)
-#'
-#' # Obtain R0 when the serial distribution has a mean of five days.
-#' ID(NT, mu = 5 / 7)
-#'
-#' # Obtain R0 when the serial distribution has a mean of three days.
-#' ID(NT, mu = 3 / 7)
-#'
-#' @export
-ID <- function(NT, mu) {
- NT <- as.numeric(NT)
- TT <- length(NT)
- s <- (1:TT) / mu
- y <- log(NT) / s
-
- R0_ID <- exp(sum(y) / TT)
-
- return(R0_ID)
-}