# qqsl: Quantile-Quantile plot against the skew logistic distribution In sld: Estimation and Use of the Quantile-Based Skew Logistic Distribution

## Description

`qqgl` produces a Quantile-Quantile plot of data against the quantile-based skew logistic distribution, or a Q-Q plot to compare two sets of parameter values for the quantile-based skew logistic distribution. This function does for the skew logistic distribution what `qqnorm` does for the normal.

## Usage

 ```1 2``` ```qqsl(y=NULL,parameters1,parameters2=NULL,abline=TRUE, granularity.for.2.dists=4000,use.endpoints=FALSE,...) ```

## Arguments

 `y` The data sample `parameters1` A vector of length 3, containg the parameters of the skew logistic distribution, alpha, beta and delta. `parameters2` Second set of parameters of the skew logistic distribution. A vector of length 3, as described above for `parameters1`. `abline` A logical value, TRUE adds a line through the origian with a slope of 1 to the plot `granularity.for.2.dists` Number of quantiles to use in a Q-Q plot comparing two sets of parameter values `use.endpoints` logical. When comparing two sets of parameter values, should Q(0) and Q(1) be used? TRUE will give QQ plots including the theoretical minimum and maximum of the distribution, which is arguably not equivalent to what would be seen in QQ plots based on data. FALSE will give QQ plots based on ideal depths (type 8 quantiles, see `quantile` documentation), where `n` is the `granularity.for.2.dists`. `...` graphical parameters, passed to `qqplot`

## Details

See `sld` for more details on the Skew Logistic Distribution. A Q-Q plot provides a way to visually assess the correspondence between a dataset and a particular distribution, or between two distributions.

## Value

A list of the same form as that returned by `qqline`

 `x` The x coordinates of the points that were/would be plotted, corresponding to a skew logistic distibution with parameters alpha, beta and delta. `y` The original `y` vector, i.e., the corresponding y coordinates, or a corresponding set of quantiles from a skew logistic distribution with the second set of parameters

## Author(s)

Robert King, [email protected], http://tolstoy.newcastle.edu.au/~rking/ and Paul van Staden

## References

van Staden, P.J. and King, R.A.R. (2015) The quantile-based skew logistic distribution, Statistics and Probability Letters 96 109–116. http://dx.doi.org/10.1016/j.spl.2014.09.001

van Staden, Paul J. 2013 Modeling of generalized families of probability distribution in the quantile statistical universe. PhD thesis, University of Pretoria. http://hdl.handle.net/2263/40265

`sld`

## Examples

 ```1 2``` ```qqsl(y=rsl(100,c(0,1,0.7)),parameters1=c(0,1,0.7)) qqsl(parameters1=c(0,1,0.7),parameters2=c(0,0.9,0.5),col="blue") ```

### Example output

```Loading required package: lmom
```

sld documentation built on May 2, 2019, 5:53 a.m.