Cronbach's Alpha Explained: Formula, Worked Example, Python/R Code, and a Free Calculator
You built a survey with several questions that are supposed to measure the same thing (say, "job satisfaction" or "stats anxiety"). Before you avera…
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DemoDoctor: Bad Robot Demonstrations Are Detectable. Do They Matter?
Inject known faults into robot demonstrations, detect them without labels, and measure what they cost a policy. The honest answer so far: I could no…
A Curve Fitter That Refuses to Answer
Code: Megapixel99/undetermined Plenty of libraries fit a curve to measurements and hand you back a number. undetermined hands back a number with the…
My Comment Section Designed My Next Experiment. Then It Made Me Freeze My Predictions.
Ten days ago I published an article about a failure mode: tell a language model "a scanner flagged this code" and some models agree with everything.…
NBA play-in odds are not playoff odds: simulating the play-in tournament instead of guessing it
In baseball, American football and hockey, "make the playoffs" is one line: finish above it and you're in. When I built an NBA version of my playoff…
Correct score, BTTS and Over/Under probabilities with Dixon-Coles: what I learned building it for MLS and Liga MX
Most football prediction pages give you three numbers — home, draw, away — and no way to check where they came from. I wanted the opposite: one mode…
Multi-Armed Bandit Testing: How It Works and When to Use
A multi-armed bandit is an algorithm that decides how to split traffic across several variations while a test is still running, shifting more visito…
How to Choose a Minimum Detectable Effect (MDE)
You have opened your sample-size calculator, entered your baseline conversion rate, kept the defaults for significance and power, and now the calcul…
You Don't Need a Math PhD for Data Science — You Need to Stop Skipping the Boring Step
Ask someone switching into data science what worries them and it's almost always the same thing: do I know enough math? So they spend weeks on gradi…
I read the metric libraries of five widely-used eval tools. The metric was never the hard part.
Every LLM eval tool sells you the same headline: a big bag of ready-made metrics. Fifty of them. Seventy. Pick one, call evaluate(), get a number. T…
Your eval monitor fired on four days this week. At your sample size, that was the most likely count
A team I compared notes with recently runs continuous evals on production traffic: an LLM judge scores a sample of traces, the scores land on a dash…
Your A/B test has three goals and they disagree. Now what?
Every A/B testing tutorial ends the same way: run the test, wait for significance, ship the winner. Then you run a real test and variant B converts…
Meta-Analysis: Between-Study Heterogeneity
Adapted from an appendix of my MS thesis. Between-Study Heterogeneity The extent to which true effect sizes vary within a meta-analysis is called be…
Markov Chain Monte Carlo: Theoretical Foundations
Adapted from an appendix of my MS thesis. Markov Chain Monte Carlo Almost as soon as computers were invented, they were used for simulation. Markov…
When SuSiE Says '95% Confident', Is It?
Benchmarking the Honesty of Fine-Mapping Credible Sets Fine-mapping has a promise built into its output, and almost nobody checks whether the promis…
A model with R-squared near 0 can still give valid 90% prediction intervals - here's why (and the catch)
I recently calibrated a recovery-rate model that had only two weak features. Its point accuracy was almost nothing — R² basically zero. I expected i…
Stop Shipping ML Models With Bare Floats: A Deep Dive Into Statistically Rigorous Model Evaluation
Stop Shipping ML Models With Bare Floats Every week, somewhere, a team makes a deployment decision that looks like this: Model A: AUROC = 0.847 Mode…
A Scatter-Plot Explorer for World Statistics — Log Scales and Hand-Rolled Pearson Correlation
"Do countries with higher GDP per capita also have longer life expectancy?" I built a tool that lets you explore questions like that across 48 count…
Graduate Statistics Problem Sets
I put my coursework from SIUe's Master's in Mathematics program up on the problem sets section of this site. Five courses from 2021-2022 that formed…
I Built CausalLens — A Free, Open-Source Causal Impact Calculator for Time Series (5 Methods, Zero Setup)
I want to show you a tool I just open-sourced. It's called CausalLens, and it answers one specific question that most analytics stacks get completel…
Cointegration and Pairs Trading: When Time Series Move Together
Pairs trading rests on a simple idea: find two assets that move together, wait for them to diverge, and bet on convergence. The hard part is definin…
Lending's Old Faithful: How a 1958 Breakthrough Still Holds Off the AI Rush
Series: Building an Explainable AI Underwriter This is Part 2 . ↜ Part 1: Why Explainable AI Matters in Underwriting ↝ Part 3: Human Intervention Th…