# effect: Draw a change in the probability distribution on an existing... In plot3logit: Ternary Plots for Trinomial Regression Models

## Description

Given the first two probabilities of a trinomial distribution before and after a change, `effect()` adds an arrow to an existing ternary plot. If the probability distribution does not change, a point (instead of an arrow) is added to the plot.

## Usage

 `1` ```effect(x, y, ..., length = 0.05) ```

## Arguments

 `x, y` `numeric` vectors of the first two probabilities. If the probability distribution is unchanged, `x` and `y` should have length one. `...` other graphical parameters such as `xpd` and the line characteristics `lend`, `ljoin` and `lmitre`. See `graphics::par()`. `length` length of the edges of the arrow head (in inches).

## Warning

Only when `effect()` is passed to `Ternary::AddToTernary()` as the first argument, arrows and points are drawn consistently with ternary coordinate system, otherwise `effect` draws both arrows and points according to a Cartesian coorinate system centered on (0,0.5,0.5).

## Examples

 ``` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15``` ```TernaryPlot() # Arrow plot3logit:::effect(c(0.1, 0.2), c(0.3, 0.2)) # Point plot3logit:::effect(0.3, 0.2) # Compare the two coordinate systems plot3logit:::effect(0.1, 0.2, pch = 19, col = 'red') AddToTernary(plot3logit:::effect, list(c(0.1, 0.2, 0.7)), pch = 19, col = 'blue') # The origin of Cartesian coordinate systems plot3logit:::effect(0, 0, pch = 19, col = 'red') AddToTernary(plot3logit:::effect, list(c(0, 0.5, 0.5)), pch = '+', col = 'white') ```

plot3logit documentation built on Feb. 26, 2021, 5:06 p.m.