Statistics · Probability · Data
Stats & Cats
The cats are illustrative. The statistics are real.
Statistical concepts explained clearly, tools that actually help, and cats doing maths. Data concepts, statistical thinking, probability — written for people who want to understand what's going on, not just be handed a formula.
Statistical ideas and how they connect to real decisions, explained without hand-waving.
Calculators and interactive helpers for working through data problems yourself.
A growing wiki of statistical terms, tests, and techniques to look things up.
Calculators & Tools
- NewCat Population Simulator
Watch a feral cat colony evolve over ten simulated years. Configure TNR programs, food availability, and coat distributions, then see what the statistics show.
- Descriptive Statistics
Mean, median, mode, standard deviation, quartiles, skewness, kurtosis, and a histogram for any dataset.
- Pearson Correlation
Compute r, r², and a two-tailed p-value for two paired numeric series, with a scatter plot and regression line.
- Independent Samples t-Test
Test whether two groups differ significantly using Welch's t-test, with confidence interval and density curves.
- Chi-Square Goodness of Fit
Test whether observed category counts match a hypothesized distribution.
- Binomial Probability
Exact, cumulative, and complementary probabilities for a binomial distribution, with a full PMF chart.
From the blog
All posts →The Central Limit Theorem: Why Averages Behave
Individual observations can follow nearly any distribution. Average enough of them together, and the result converges toward normal. Here's why that happens and why it matters.
Regression to the Mean: Why Exceptional Performance Doesn't Last
Extreme outcomes tend to be followed by more ordinary ones. This is not a psychological phenomenon. It is a mathematical one, with real implications for how we evaluate causes and interventions.
What Confidence Intervals Actually Tell You
A 95% confidence interval does not mean a 95% probability that the true value is inside it. Here is what the statement actually means, and why the distinction is worth getting right.
The Base Rate Fallacy: When a Positive Test Isn't Good Evidence
A 99% accurate test for a rare condition still leaves you more likely than not to be healthy after a positive result. Bayes' theorem explains why the prior matters.
Correlation Is Not Causation, Illustrated With Cat Food
A study shows premium cat food extends feline life. It probably doesn't. A walkthrough of confounders, causal DAGs, and collider bias: the machinery behind each illusion.