plot.htest {NCStats} R Documentation

## Plots test statistic and p-value area for z-, t-, and chi-square tests.

### Description

Plots test statistic and p-value area for z-, t-, and chi-square tests.

### Usage

```## S3 method for class 'htest'
plot(x, smoothness = 1000, shade.col = "red",
```

### Arguments

 `x` an object saved from `z.test`, `t.test`, or `chisq.test` `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 (primary) shaded area. If the alternative is two.sided then this area is in the same tail as the test statistic `shade.col2` a string indicating the color to use for the (secondary) shaded area. If the alternative is two.sided then this area is in the opposite tail as the test statistic `...` optional arguments that are not implemented in this version

### Details

This produces a plot of the named sampling distribution with the test statistic and p-value areas shown. This plot is used primarily for students to visualize the calcualtion of the p-value in the `z.test`, `t.test`, and `chisq.test` functions. The results from those functions must be saved to an object.

### Value

None. However, a plot is constructed.

### Note

Newbie students can benefit greatly from visualizing the position of the test statistic and the “area” of the p-value for common statistical tests using the z-, t-, and chi-square tests. This function produces a graphic from the results of `z.test`, `t.test`, and `chisq.test` to show these values. An additional benefit of this function is that newbie students make fewer mistakes in choosing the alternative hypothesis when they can visualize the final result.

`z.test`, `t.test`, and `chisq.test`.

### Examples

```## 1-sample z-test example
z.ex <- z.test(rnorm(25,100,5),99,5)
z.ex
plot(z.ex)

## 1-sample t-test example from t.test
t1.ex <- t.test(1:10,y=c(7:20))
t1.ex
plot(t1.ex)

## 2-sample t-test example from t.test
t2.ex <- t.test(extra~group,data=sleep)
t2.ex
plot(t2.ex)

## same but with one-tailed alternative (for illustration)
t3.ex <- t.test(extra~group,data=sleep,alt="less")
t3.ex
plot(t3.ex)

## Chi-square test example from chisq.test
chi1.ex <- chisq.test(InsectSprays\$count > 7, InsectSprays\$spray)
chi1.ex
plot(chi1.ex)

## Another Chi-square test example from chisq.test
x <- matrix(c(12, 5, 7, 7), ncol = 2)
chi2.ex <- chisq.test(x)
chi2.ex
plot(chi2.ex)

## Another Chi-square test example from chisq.test
x <- c(89,37,30,28,2)
p <- c(40,20,20,15,5)
chi3.ex <- chisq.test(x, p = p, rescale.p = TRUE)
chi3.ex
plot(chi3.ex)

```

[Package NCStats version 0.4.7 Index]