Data for Exercise 7.55

`Coffee`

A data frame/tibble with nine observations on three variables

- without
workers' productivity scores without a coffee break

- with
workers' productivity scores with a coffee break

- differences
`with`

minus`without`

Kitchens, L. J. (2003) *Basic Statistics and Data Analysis*.
Pacific Grove, CA: Brooks/Cole, a division of Thomson Learning.

```
qqnorm(Coffee$differences)
qqline(Coffee$differences)
shapiro.test(Coffee$differences)
#>
#> Shapiro-Wilk normality test
#>
#> data: Coffee$differences
#> W = 0.89448, p-value = 0.2217
#>
t.test(Coffee$with, Coffee$without, paired = TRUE, alternative = "greater")
#>
#> Paired t-test
#>
#> data: Coffee$with and Coffee$without
#> t = 1.1767, df = 8, p-value = 0.1366
#> alternative hypothesis: true difference in means is greater than 0
#> 95 percent confidence interval:
#> -0.580312 Inf
#> sample estimates:
#> mean of the differences
#> 1
#>
wilcox.test(Coffee$with, Coffee$without, paired = TRUE,
alterantive = "greater")
#> Warning: cannot compute exact p-value with ties
#> Warning: cannot compute exact p-value with zeroes
#>
#> Wilcoxon signed rank test with continuity correction
#>
#> data: Coffee$with and Coffee$without
#> V = 25.5, p-value = 0.324
#> alternative hypothesis: true location shift is not equal to 0
#>
```