Descriptive Statistics

Descriptive stats summarise a dataset: MEAN, MEDIAN, MODE (centre); RANGE, VARIANCE, STANDARD DEVIATION (spread); MIN, MAX, QUARTILES.

Always look at both centre and spread — a single number hides a lot.

Example 1 (python)

import numpy as np
x = np.array([5, 7, 8, 9, 10, 12, 100])
print(np.mean(x), np.median(x), np.std(x))

Output

21.57 9.0 32.51

One outlier pulls the mean up.

Example 2 (python)

import pandas as pd
pd.Series(x).describe()

Output

count 7
mean 21.57 ...

.describe() gives a full summary.

Key points

💡 Note: When mean >> median, your data is skewed — investigate outliers before modelling.