The Test Set by Posit

Posit CEO Tareef Kawaf’s theory about LLMs is that they work like an exponent on whoever you already are. Greater than one and you compound. Under one and you accelerate in the wrong direction. Michael, Wes, and Hadley chat with Tareef about what that means for data science, along with John Chambers' Prime Directive, why Tareef now goes up against his own board, and the cat he waited 40 years for.

What’s Inside
LLMs as an exponent, and why the base is you
The CEO bug hunter
John Chambers' Prime Directive and why AI makes it matter again
A Kaypro 16, 128K of RAM, and an uncle in Daytona
The 70 percent of your job that stops being yours
The oud, and the cat he waited forty years for

Leland McInnes has spent his career building tools a lot data scientists take for granted (UMAP, HDBSCAN), and amusingly the applications of those tools keep getting stranger. On this episode of The Test Set, he tells Michael, Hadley, and Wes about teams tracking laundered gold through mineral impurities, and the time he helped casinos optimize slot machine layouts. Also, why nobody's intuition survives contact with high-dimensional space. On this episode of The Test Set, we hit all that, plus imposter syndrome, AI as a sounding board, and the case for asking better questions instead of chasing answers.
What's inside
Wild UMAP use cases, e.g., catching laundered gold
Why casinos pay mathematicians to rearrange slot machines
High-dimensional space and how it defies human intuition
Neural embeddings for people who aren't AI researchers
Imposter syndrome — across two disciplines
Leland’s take on AI as a rubber-duck testing partner
“Look at your data" because it legit beats guessing

Ruth Milligan has coached hundreds of conference speakers, curates TEDx Columbus, and wrote The Motivated Speaker. She's here to tell you that speaking is habitual, not natural. Michael, Wes, and Hadley get a live fifteen-second filler word hack, an uncomfortable truth about listening back to your own voice, and the three kinds of pitches Ruth has been reading for seventeen years.
What's inside
Why a great idea beats a great speaker
Speaking is habitual, not natural, and that’s good
The fifteen-second breathing trick to kill fillers
How many charts do you need? Fewer than you think
The three pitches Ruth has read for seventeen years
You can't get better until you listen to yourself
Hadley contends people who send voice memos are monsters
Mentioned in this episode
Patsy Rodenburg's "Three Circles of Energy" — a summary of the framework
Rébecca Kleinberger, "Why you don't like the sound of your own voice" (TED)

Trevor Manz went from measuring plant apertures by hand in a wet lab to building the notebook that lets coding agents take the wheel. The creator of anywidget and founding engineer at marimo (marimo.io/pair) popped into The Test Set to spill on reactive notebooks, why marimo pair threw out every MCP tool but one, and what agents really want out of a data environment. This conversation also features a jacket bouncer, a hidden Python API, and Michael's slow-motion war with the word "marimo."
What's inside:
Cell order doesn't matter in a reactive Python notebook
Wet-lab pipettes and Harvard's visualization group, via Raspberry Pi
The problem with building beautiful tools nobody actually uses
The reason marimo pair deleted every agent tool but one
Code mode: the hidden API humans aren't supposed to touch
What happens when you ship the API your LLM hallucinated

Leilani Battle studies how software shapes what we see and believe. The University of Washington professor and co-director of the UW Interactive Data Lab talks with Michael, Hadley, and Wes about an experiment that manipulated people using nothing but loading speed, and why AI models don't seem to recommend charts the way the community that studies charts actually does. Other highlights: rationality's blind spots and a thorough disc golf origin story.
What's inside:
Loading spinners that quietly change what people find
AI models that don't recommend charts like humans do
The blurry line between databases and human factors
A behavior-change experiment for building fairer models
Rationality's role in producing unethical outcomes
Disc golf origin story
A vegan pancake recipe