Case Study 1 — Redesigning Lena's Results Slide, Assertion–Evidence

A composite, fictional-but-realistic walkthrough. Dr. Lena Foss is presenting her solid-state-battery result at a conference. We saw the principle in §18.2; here we slow down and rebuild one slide — her single most important one, the key result — from the topic-and-bullets version she first made into the assertion–evidence version that actually lands. Watch each design decision do its job.

The slide she built first

Lena opened her paper, found the results figure, and pasted it onto a slide with the surrounding text turned into bullets. This is what 90% of researchers do, and here is what it produced:

Slide (described): "Results." Title, top-left, in 20-point type: Results Body — six bullets in 18-point text: - Novel sulfide-based interphase synthesized via solution coating - Capacity retention of 94% measured after 800 charge–discharge cycles at 0.5C - Comparison to LiPON baseline: 80% retention after 500 cycles - Coulombic efficiency improved from 99.1% to 99.7% - Interfacial resistance reduced by approximately 40% - Cross-sectional SEM (inset, bottom-right) shows uniform 50 nm interphase layer Bottom-right: a thumbnail electron-microscope image, roughly 4 cm wide, with a scale bar too small to read from a seat.

Read it the way the audience will. A listener glances up, reads all six bullets in about eight seconds — faster than Lena can speak them — and then sits there, slightly bored, ahead of the speaker, waiting for her to catch up to the slide they've already finished. The one number that matters, the 94%-vs-80% comparison that is the contribution, is the second bullet among six equals, with no visual weight. The SEM thumbnail, the only actual picture, is too small to see. And because the slide says one set of words while Lena's mouth says another, the two streams interfere and the audience retains neither cleanly. The science on this slide is a genuine advance. The slide buries it.

Diagnose it against the chapter: - The headline ("Results") is a topic, not an assertion — it states the subject and no point (§18.2). The audience has to extract the message themselves, while listening, which they can't. - The body is text, so it triggers reading and shuts off listening (§18.1). Death by PowerPoint in miniature. - The most important comparison has no visual prominence — it's a bullet, equal in weight to the resistance footnote. - The only visual is decorative-sized, illegible from the room.

The redesign

Lena rebuilds the slide around one question: what is the single point this slide must make? The answer is her whole contribution in one claim — the new interphase nearly doubles cycle life. That becomes the headline. Then the body becomes the one visual that proves it. Everything else moves into her voice.

Slide (described), assertion–evidence: Headline band, across the top, 26-point, one line: "Our sulfide interphase holds 94% of capacity after 800 cycles — the previous best held 80% after 500." Body — a single line chart filling the slide: x-axis cycle number (0 to 800), y-axis capacity retention (%), starting at 0 so the bars/curves don't lie (Chapter 9). Two curves: Lena's, high and nearly flat, extending far to the right; the LiPON baseline, dropping off sharply and ending early near cycle 500. Each curve is labeled directly on the plot ("This work" and "LiPON baseline") — no separate legend to ping-pong to. The vertical gap between the two endpoints is lightly shaded and annotated "+14 points, +300 cycles." Large, readable axis labels. No bullet list anywhere. What Lena says while this is on screen: "The improvement isn't only cycle life — coulombic efficiency rose from 99.1 to 99.7 percent, and interfacial resistance dropped about 40 percent — and a cross-section shows the interphase forms a clean, uniform fifty-nanometer layer, which I'll show on the next slide."

Now the experience is completely different. The audience reads one sentence — the claim — in two seconds, then drops their eyes to one picture that demonstrates it, and Lena's voice fills in the supporting numbers without competing with any on-screen text. The picture is big enough to read from the back. The gap between the two curves is the visual point of the slide, so even someone who glanced up from their phone for a second sees the message: the new curve stays up; the old one falls. The SEM moved to its own slide, where it can be large enough to actually see, with its own assertion headline.

Side by side

What this teaches

The data did not change between the two slides. The molecule, the 94%, the 800 cycles, the SEM — all identical. What changed is that the redesign respects how a live audience actually works: it gives them one claim to read and one image to see, and it moves everything else into the channel (the voice) that can carry it without interference.

Notice, too, the discipline the assertion headline forced. To write "Our sulfide interphase holds 94% of capacity after 800 cycles — the previous best held 80% after 500," Lena had to decide what this slide was for and commit to a single point. The "Results" version let her dodge that decision — it was just a bucket of true statements. Writing the sentence is how she discovered which of the six bullets was the contribution and which five were support. That is Chapter 1's thesis operating at the level of a single slide: phrasing the claim clearly is how you find out whether you have one.

Try it yourself. Take the next slide Lena needs — the SEM micrograph she promised. Its topic version would be titled "Microstructure." Write its assertion headline instead: what is the one point the cross-section image makes? (Hint: it's not "here is an image"; it's something the image proves about the interphase — uniformity, thickness, the absence of cracks.) Then you've designed two assertion–evidence slides in a row, and you can feel the talk becoming a sequence of claim, proof; claim, proof — which is exactly what a clear talk is.

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