# GrowthRates: Calculates growth rates (AGR, PGR, RGRdiff) between pairs of... In growthPheno: Plotting, Smoothing and Growth Trait Extraction for Longitudinal Data

## Description

Calculates either the Absolute Growth Rate (AGR), Proportionate Growth Rate (PGR) or Relative Growth Rate (RGR) between pairs of time points, the second of which is `lag` positions before the first. in `x`.

## Usage

 ```1 2 3``` ```AGRdiff(x, time.diffs, lag=1) PGR(x, time.diffs, lag=1) RGRdiff(x, time.diffs, lag=1) ```

## Arguments

 `x` A `numeric` from which the growth rates are to be calculated. `time.diffs` a `numeric` giving the time differences between successive values in `x`. `lag` A `integer` specifying, for the second value in the pair to be operated on, the number positions it is ahead of the current value.

## Details

The AGRdiff is calculated as the difference between a pair of values divided by the `time.diffs`. The PGR is calculated as the ratio of a value to a second value which is `lag` values ahead of the first in `x` and the ratio raised to the power of the reciprocal of `time.diffs`. The RGRdiff is calculated as the `log` of the PGR and so is equal to the difference between the logarithms of a pair of values divided by the `time.diffs`. The differences and ratios are obtained using `calcLagged` with `lag = 1`.

## Value

A `numeric` containing the growth rates which is the same length as `x` and in which the first `lag` values `NA`.

## Author(s)

Chris Brien

`intervalGRaverage`, `intervalGRdiff`, `splitContGRdiff`, `splitSplines`, `calcLagged`
 ```1 2``` ```data(exampleData) longi.dat\$Area.AGR <- with(longi.dat, AGRdiff(Area, time.diffs = Days.diffs)) ```