Descriptive statistics

Summarize a dataset so patterns are visible — before you try to generalize to a larger population.

Descriptive statistics describe the data you have. Inferential statistics go further and say something careful about a larger population. Start with description.

Statistic

Any number computed from data: mean, standard deviation, median, max, …

Two questions almost always matter:

Central tendency — what is a typical value?
Dispersion — how spread out are the values?

Two datasets, same story?

Dataset $A$ is exam scores tightly clustered around 70. Dataset $B$ also averages 70 but ranges from 20 to 100. A single number (the mean) hides that difference — you need a spread measure too.

Key takeaways

Statistic = number computed from data.
Describe before you infer.
Always think “centre + spread”.