## Course description

The **t-test** can be defined as a statistical test used to compare two means. This guide provide multiple tutorials describing the different types of t-test, including:

*one-sample t-tests*. Compares one-sample mean to a know standard mean.*independent samples t-tests: Student’s t-test and Welch’s t-test*. Compares two independent groups*paired samples t-test*. Compares two related samples.

You will learn the *t-test formula* and how to:

**Compute the different t-tests in R****Check t-test assumptions****Calculate and report t-test effect size**using*Cohen’s d*.

Contents:

#### Related Book

Practical Statistics in R II - Comparing Groups: Numerical Variables## Prerequisites

Make sure you have installed the following R packages:

`tidyverse`

for data manipulation and visualization`ggpubr`

for creating easily publication ready plots`rstatix`

provides pipe-friendly R functions for easy statistical analyses.`datarium`

: contains required data sets for this chapter.

Start by loading the following required packages:

```
library(tidyverse)
library(ggpubr)
library(rstatix)
```

## Examples of R codes

Comparing two independent groups:

```
# Data preparation
data("genderweight", package = "datarium")
head(genderweight, 3)
```

```
## # A tibble: 3 x 3
## id group weight
## <fct> <fct> <dbl>
## 1 1 F 61.6
## 2 2 F 64.6
## 3 3 F 66.2
```

```
# Statistical test
stat.test <- genderweight %>%
t_test(weight ~ group) %>%
add_significance()
stat.test
```

```
## # A tibble: 1 x 9
## .y. group1 group2 n1 n2 statistic df p p.signif
## <chr> <chr> <chr> <int> <int> <dbl> <dbl> <dbl> <chr>
## 1 weight F M 20 20 -20.8 26.9 4.30e-18 ****
```

```
# Visualization:
# Create a box-plot
bxp <- ggboxplot(
genderweight, x = "group", y = "weight",
ylab = "Weight", xlab = "Groups", add = "jitter"
)
# Add p-value and significance levels
stat.test <- stat.test %>% add_xy_position(x = "group")
bxp +
stat_pvalue_manual(stat.test, tip.length = 0) +
labs(subtitle = get_test_label(stat.test, detailed = TRUE))
```

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