Lesson 2

Welcome back! This lesson is all about descriptive statistics and understanding the various characteristics of the `Titanic`

dataset.

So, why do we need to study statistics when dealing with data? Well, statistics is a branch of mathematics dealing with data collection, organization, and interpretation. In data science, we use statistics to extract meaningful insights and knowledge from data.

Statistics helps us deal with the data's complexity by reducing a complex dataset into a simpler summary. It assists in the presentation and visualization of the data, thereby making our data analysis or machine learning model more precise.

Take our current dataset, for instance, which comprises various demographics and passenger information; wouldn't it be interesting to know the average age or to gauge the variety in travelers' fares? Our lesson will focus on extracting these primary statistical features from our dataset, helping us better comprehend the `Titanic`

voyage.

Descriptive statistics summarise and organize the characteristics of a data set. A data set is a collection of responses or observations from a sample or entire population.

In pandas, there's a function called `describe()`

, which calculates the basic statistics for all continuous variables, i.e., types of variables that can take on an infinite number of values within a specific range. It provides the count, mean, standard deviation (std), min, quartiles, and max in its output.

Firstly, let's import the libraries we will be using and load the dataset:

Python`1import seaborn as sns 2 3# Load the dataset 4titanic = sns.load_dataset('titanic') 5 6# show the first few rows of data 7print(titanic.head())`

The output of the `head`

command will be like this:

Markdown`1 survived pclass sex age ... deck embark_town alive alone 20 0 3 male 22.0 ... NaN Southampton no False 31 1 1 female 38.0 ... C Cherbourg yes False 42 1 3 female 26.0 ... NaN Southampton yes True 53 1 1 female 35.0 ... C Southampton yes False 64 0 3 male 35.0 ... NaN Southampton no True`

The `describe()`

function can then be executed as follows:

Python`1# Generate descriptive statistics 2titanic_stats = titanic.describe() 3print(titanic_stats)`

The output of the `describe()`

function will be like this:

`Markdown````
1 survived pclass age sibsp parch fare
2count 891.000000 891.000000 714.000000 891.000000 891.000000 891.000000
3mean 0.383838 2.308642 29.699118 0.523008 0.381594 32.204208
4std 0.486592 0.836071 14.526497 1.102743 0.806057 49.693429
5min 0.000000 1.000000 0.420000 0.000000 0.000000 0.000000
625% 0.000000 2.000000 20.125000 0.000000 0.000000 7.910400
750% 0.000000 3.000000 28.000000 0.000000 0.000000 14.454200
875% 1.000000 3.000000 38.000000 1.000000 0.000000 31.000000
9max 1.000000 3.000000 80.000000 8.000000 6.000000 512.329200
```

In this code snippet, the `describe()`

function generates descriptive statistics that summarize a dataset's distribution's central tendency, dispersion, and shape, excluding `NaN`

values.

Notice how all the categorical columns, like `'sex'`

or `'class'`

, are missing in the output. By default, `describe()`

only includes columns with numerical data.

If you want to include all columns, you need to pass `include='all'`

as an argument. Here is how to do it:

Python`1# Generate descriptive statistics 2titanic_stats = titanic.describe(include='all') 3print(titanic_stats)`

Note that for categorical variables, the output has different features – unique, top, and freq. `'unique'`

shows the number of distinct objects in the column, `'top'`

shows the most frequent object, and `'freq'`

shows how many times the top object appears in the column.

Variability, also known as dispersion, is the extent to which data points differ from the center. Two commonly used measures are the **range** and **interquartile range (IQR)**.

The **range** is the difference between a dataset's maximum and minimum values. However, it's sensitive to outliers; extremely high or low values can skew the range. Here's how you calculate the range for the `age`

column of the Titanic dataset:

Python`1# Calculate the numerical data range 2age_range = titanic['age'].max() - titanic['age'].min() 3print('Age Range:', age_range) # Age Range: 79.58`

The **IQR** measures statistical dispersion, or how far apart the data points are. It's the range within which the middle 50% of your data falls. It's a better measure of dispersion than the range because outliers don't affect it. Here's how you can calculate it:

Python`1# Calculate the IQR 2Q1 = titanic['age'].quantile(0.25) 3Q3 = titanic['age'].quantile(0.75) 4IQR = Q3 - Q1 5print('Age IQR:', IQR) # Age IQR: 17.875`

Central tendency measures help you find the center of your dataset. Mean and median are the most common measures of central tendency.

The **mean** or average is the most common measure of central tendency. It's the sum of all data points divided by the number of data points.

Python`1# Calculate the mean 2mean_age = titanic['age'].mean() 3print('Mean Age:', mean_age) # Mean Age: 29.69911764705882`

The **median** is the middle score. The scores must be arranged in numerical order to identify the median correctly.

Python`1# Calculate the median 2median_age = titanic['age'].median() 3print('Median Age:', median_age) # Median Age: 28.0`

You've just taken your first steps into the realm of descriptive statistics! In this lesson, you've learned about the usefulness of statistics in data analysis and how we can summarize our `Titanic`

dataset via central tendency and dispersion measures.

Hence, understanding these statistical characteristics and central tendencies is significant for making effective predictions about our dataset, offering a sound foundation for building meaningful data visualizations.

With the theory presented, let's put that into practice! This practice exercise will help you revisit everything learned in this lesson while drawing out statistical inferences from our `Titanic`

dataset.