In jrminter/statshelpR: Convenience functions for statistical analysis

knitr::opts_chunk$set(echo = TRUE, warning=FALSE)
suppressWarnings(suppressMessages(suppressPackageStartupMessages(library(ggplot2))))

Introduction

This example is adapted from data supplied by Ron Larson and Betsy Faber, Elementary Statistics Picturing the World, 6th edition, in Chapter 6 p. 344.

A vendor claims that the variation of a batch of washers is within $\pm 0.002$ in. The customer measured the thickness of 15 randomly selected washers and reported the data (in inches) below.

dat <- c(0.422, 0.424, 0.424, 0.430, 0.419,
         0.424, 0.420, 0.424, 0.425, 0.425,
         0.423, 0.431, 0.437, 0.422, 0.434)

Does this sample of washers meet the variance criterion at the 95% confidence level? We will compute the 95% confidence interval of our sample.

library(statshelpR)
library(knitr)

df <- var_interval(dat, 0.002, 0.95)
kable(df)

Summary

Note that the 95% confidence interval for the standard deviation r df$Value[7] - r df$Value[6] and does not contain 0.002. Therefore the batch us unacceptable.

jrminter/statshelpR documentation built on May 2, 2020, 12:08 a.m.