plot.htest {NCStats} | R Documentation |

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

## S3 method for class 'htest' plot(x, smoothness = 1000, shade.col = "red", shade.col2 = "red3", ...)

`x` |
an object saved from |

`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 |

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.

None. However, a plot is constructed.

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`

.

## 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 0.4.4 Index]