distrib {NCStats} | R Documentation |

Plots calculated areas or values from normal, Student's t, F, chi-square, beta, exponential, and gamma continuous density functions and binomial, geometric, negative binomial, Poisson, and hypergeometric discrete distribution functions.

distrib(val, distrib = c("norm", "t", "chisq", "f", "beta", "exp", "gamma", "pois", "binom", "geom", "hypergeom", "nbinom"), type = c("p", "q", "d", "forward", "reverse"), digits = getOption("digits"), mean = 0, sd = se, se = 1, df = 1, df1 = df, df2 = 1, shape1 = 1, shape2 = 1, shape = 1, rate = 1, scale = 1/rate, size = 10, prob = 0.5, mu = NULL, lambda = 1, m = NULL, n = NULL, k = NULL, lower.tail = TRUE, plot = TRUE, show.ans = TRUE, show.alt = FALSE, main = NULL, xlab = NULL, ylab = NULL, yaxt = "n", smoothness = 1000, shade.col = "red", shade.trans = 1, lbl.col = "red", ...)

`val` |
a single-length numeric containing a value or probability/quantile. |

`distrib` |
a string indicating the type of distribution to use. See details. |

`type` |
a string indicating the type of calculation to make – |

`digits` |
A numeric indicating the number of decimals to round the returned result when |

`mean` |
a single-length numeric for the mean of the normal distribution. |

`sd` |
a single-length numeric for the standard deviation of the normal distribution. |

`se` |
a single-length numeric for the standard error of the normal distribution (see details) |

`df` |
a single-length numeric for the degrees-of-freedom for the t and chi-square distributions. |

`df1` |
a single-length numeric for the numerator degrees-of-freedom for the F distribution. |

`df2` |
a single-length numeric for the denominator degrees-of-freedom for the F distribution. |

`shape1` |
a single-length numeric for the first shape parameter in the beta distribution. |

`shape2` |
a single-length numeric for the first shape parameter in the beta distribution. |

`shape` |
a single-length numeric for the shape parameter in the gamma distribution. |

`rate` |
a single-length numeric for the rate parameter in the gamma and exponential distributions. See details. |

`scale` |
a single-length numeric for the scale parameter in the gamma distribution. |

`size` |
a single-length numeric for the number of trials in the binomial distribution. |

`prob` |
a single-length numeric for the probability of success on each trial in the binomial, geometric, and negative binomial distributions. |

`mu` |
a single-length numeric for the mean of negative binomial distribution. see details |

`lambda` |
a single-length numeric for the mean of the Poisson distribution. |

`m` |
a single-length numeric for the number of white balls in the urn of a hypergeometric distribution. |

`n` |
a single-length numeric for the number of black balls in the urn of a hypergeometric distribution. |

`k` |
a single-length numeric for the number of balls drawn from the urn of a hypergeometric distribution. |

`lower.tail` |
a logical indicating if the probabilities are P[X<=x] ( |

`plot` |
a logical indicating if a plot should be shown ( |

`show.ans` |
a logical indicating if the computational results should be shown on the plot ( |

`show.alt` |
a logical indicating if a message showing alternaive (i.e,. traditional) code for obtaining the answer should be shown ( |

`main` |
a character string for the plot's main label. If null an appropriate string will be created. |

`xlab` |
character string for plot's x-axis label. If null an appropriate string will be created. |

`ylab` |
character string for plot's y-axis label. If null an appropriate string will be created. |

`yaxt` |
a character which specifies the y axis type. Specifying |

`smoothness` |
a single-length numeric indicating the number of points for which to construct the plot. The larger the number the smoother the plot will appear. |

`shade.col` |
a string indicating the color to use for the shaded area. |

`shade.trans` |
Value between 0 and 1 indicating the transparency to use for the shaded area. |

`lbl.col` |
a string indicating the color to use for labeling the shaded area. |

`...` |
optional parameters to send to the internal |

This function computes the same values as the `pXXX`

and `qXXX`

functions for both continuous density and discrete probability distributions and as the `dXXX`

functions for the discrete probability distributions. This function is used primarily to include a plot with the calculation. The original functions in the stats package should be consulted for more details on each distribution. For example, use `?dbinom`

to get help for computing the probability of a value in the binomial distribution, `?ppois`

to get help for computing the cumulative probability of a value on the Poisson distribution, and `?qnorm`

to get help for computing the quantile value of a normal distribution.

The strings in the `distrib`

argument are the same as the abbreviated function names in the stats package. For example, the normal distribution is `"norm"`

, the chi-square distribution is `"chisq"`

, and the hypergeometric distribution is `"hyper"`

The strings in the `type`

argument at the same as the prefixes to the abbreviated function names in the stats package. For example, the density is computed with `"d"`

, the cumulative probability with `"p"`

, and the quantiles with `"q"`

. The `"forward"`

and `"reverse"`

types correspond to `"p"`

and `"q"`

, respectively, and are used to match terminology used in the Introductory Statistics course at Northland College.

Other visualizations of the distribution can be seen with functions that are named with the `s`

prefix (for simulation) on the abbreviated function name. For example, try `sbinom()`

to show a simulation of the binomial distribution.

Note that for a normal distribution the `se=`

argument is supplied for convenience only. Whatever is supplied to `se=`

is then applied to the `sd=`

argument. Use of `se=`

may be somewhat simpler for students learning to distinguish between normal distribution calculations on a sampling versus a population distribution.

A numeric answer is returned. If `plot=TRUE`

then a plot is constructed and a note on how to use one of the functions in stats is printed if `show.alt=TRUE`

.

Students often need to “look up” values or probabilities from statistical tables in textbooks. These values can be easily found in R with the `pXXX`

, `qXXX`

, or `dXXX`

distributional functions. However, these functions do not provide a visual representation of the computation. This function also replaces the tables of distributional values found in texts but also provides a graph of the computation.

I had hoped to add a `plot=`

argument to any of the `pXXX`

, `qXXX`

, or `dXXX`

distributional functions but this required replacing the base R functions. A compromise was to create this new function, using the `type=`

argument with `p`

, `q`

, and `d`

and printing a direction on how to use the base R function if `show.alt=TRUE`

.

The `type=`

and `distrib=`

arguments can be concatenated to provide the typical function in base R. For example, for the examples below see `dbinom`

, `dpois`

, `pexp`

, and `qnorm`

.

op <- par(mfrow=c(2,2),mar=c(3.5,1,3.5,1),mgp=c(2,0.75,0)) distrib(4,distrib="binom",type="d",size=10,prob=0.5) distrib(5,distrib="pois",type="p",lambda=2) distrib(2.2,distrib="exp",type="p",rate=1/2) distrib(0.6,distrib="norm",type="q",mean=10,sd=3,lower.tail=FALSE) par(op)

[Package *NCStats* version 0.4.7 Index]