The first function is from **NumPy** and the second one is from **pandas**. Look at the example of calculating the standard deviation for the `work_year`:

import pandas as pd
import numpy as np

df = pd.read_csv('https://codefinity-content-media.s3.eu-west-1.amazonaws.com/a849660e-ddfa-4033-80a6-94a1b7772e23/update/ds_salaries_statistics', index_col = 0)

# Calculate the standard deviation using the function from the NumPy library
std_1 = np.std(df['salary_in_usd'])
# Calculate the standard deviation using the function from the pandas library
std_2 = df['salary_in_usd'].std()

print('The variace using NumPy library is', round(std_1, 2))
print('The variace using pandas library is', round(std_2, 2))

This section will help us deal with the first real statistical case: finding confidence intervals. It requires knowledge of NumPy, pandas, Matplotlib, and Seaborn library to calculate math formulas and build visualization! To encourage you to pass this section, I want to point out that you will run across a small amount of theory but a significant amount of practice!

An inseparable part of a data analyst's life is conducting hypothesis testing. After completing this section, you will understand the idea behind testing in statistics and will be able to conduct a t-test using Python.