Chapter 2 Descriptive Statistics
The exploratory data analysis, or descriptive statistics, is directly connected to the organization and description of the data. It brings together a reasonable amount of tools that can help in understanding observed values. It is used, for example, to assess how observations are distributed, where they are positioned and how they present themselves in terms of distribution and association.
In this chapter, concepts and methods of data exploration will be presented, a fundamental step for more advanced statistical analysis. For further discussion we recommend (Tukey 1977), a milestone in exploratory data analysis.
After reading this chapter, the reader should be able to interpret the following example, adapted from (Waring et al. 2022) at the suggestion of João Brito. More details at this link (in Portuguese) from Wiki R.
# Load packages
library(skimr)
library(tidyverse)
# Load data
data(starwars)
# An alternative to summary()
skimr::skim(starwars) # HTML and docx| Name | starwars |
| Number of rows | 87 |
| Number of columns | 14 |
| _______________________ | |
| Column type frequency: | |
| character | 8 |
| list | 3 |
| numeric | 3 |
| ________________________ | |
| Group variables | None |
Variable type: character
| skim_variable | n_missing | complete_rate | min | max | empty | n_unique | whitespace |
|---|---|---|---|---|---|---|---|
| name | 0 | 1.00 | 3 | 21 | 0 | 87 | 0 |
| hair_color | 5 | 0.94 | 4 | 13 | 0 | 12 | 0 |
| skin_color | 0 | 1.00 | 3 | 19 | 0 | 31 | 0 |
| eye_color | 0 | 1.00 | 3 | 13 | 0 | 15 | 0 |
| sex | 4 | 0.95 | 4 | 14 | 0 | 4 | 0 |
| gender | 4 | 0.95 | 8 | 9 | 0 | 2 | 0 |
| homeworld | 10 | 0.89 | 4 | 14 | 0 | 48 | 0 |
| species | 4 | 0.95 | 3 | 14 | 0 | 37 | 0 |
Variable type: list
| skim_variable | n_missing | complete_rate | n_unique | min_length | max_length |
|---|---|---|---|---|---|
| films | 0 | 1 | 24 | 1 | 7 |
| vehicles | 0 | 1 | 11 | 0 | 2 |
| starships | 0 | 1 | 17 | 0 | 5 |
Variable type: numeric
| skim_variable | n_missing | complete_rate | mean | sd | p0 | p25 | p50 | p75 | p100 | hist |
|---|---|---|---|---|---|---|---|---|---|---|
| height | 6 | 0.93 | 174.36 | 34.77 | 66 | 167.0 | 180 | 191.0 | 264 | ▁▁▇▅▁ |
| mass | 28 | 0.68 | 97.31 | 169.46 | 15 | 55.6 | 79 | 84.5 | 1358 | ▇▁▁▁▁ |
| birth_year | 44 | 0.49 | 87.57 | 154.69 | 8 | 35.0 | 52 | 72.0 | 896 | ▇▁▁▁▁ |