OpenIntro Statistics
A free, well-regarded introductory statistics textbook covering data, distributions, sampling, inference, hypothesis tests and regression, with videos, slides and labs. Everything an analyst needs to understand averages, uncertainty and A/B tests, explained without heavy maths.
Book
Other
OpenIntro
Self paced, a semester course
Beginner
Free
What it is
OpenIntro Statistics is an introductory statistics textbook from OpenIntro, a non-profit that publishes free, high-quality textbooks. The current edition is the 4th. The PDF is free (with an optional contribution), and printed copies cost $25 in black and white or $40 in colour (as of 2026-09, from openintro.org). OpenIntro says it is used everywhere from community colleges to Ivy League universities, and it comes with videos, slides and labs in several tools, including R and Python.
What it covers
Nine chapters: introduction to data, summarising data, probability, distributions, foundations for inference, inference for categorical data, inference for numerical data, introduction to linear regression, and multiple and logistic regression.
For an analyst, the most useful parts are:
- Summarising data: mean, median, spread, skew and outliers, and when each summary misleads.
- Sampling and study design: bias, random samples, observational studies versus experiments, which is where "correlation is not causation" comes from.
- Foundations for inference: confidence intervals and hypothesis tests, explained with intuition before formulas.
- Inference for proportions: the maths behind comparing conversion rates in an A/B test.
- Linear regression: fitting and, more importantly, interpreting a line.
Is it worth your time?
Yes. Many analysts learn tools and skip statistics, then struggle to explain whether a change in a metric is real or noise. You do not need the whole book for a first job: chapters 1, 2, 5, 6 and 8 cover most of what analysts use. The examples are clear and the exercises have answers for odd-numbered questions.
Prerequisites
School algebra. No calculus.
How to use it
Read a section, watch the matching video if you prefer, then reproduce one example in your own tool: a spreadsheet, SQL, Power BI, Tableau or pandas. Doing the calculation on real data is what makes it stick.
Common questions
Khan Academy or OpenIntro? Use Khan Academy for short explanations and practice questions, and OpenIntro for a structured, deeper read. They complement each other.
Is the free PDF the full book? Yes.
Ready to start?
Opens on OpenIntro in a new tab.
Stuck on something specific?
Writing only gets you so far. If you want an answer to your situation rather than the general case, book a session and we will work through it together. Sessions are free for approved Sefism members, and a few slots open each week.
Follow along
New writing, resources and project ideas land here first.