Designing effective slides
The default PowerPoint slide — a short topic phrase as a title, followed by a bullet list — is so familiar that almost nobody questions it. It's also, according to a substantial body of research on how people actually process visual and verbal information together, a genuinely weak way to communicate a scientific result. There's a well-tested alternative worth knowing about.
The problem with bullet-list slides
A topic-phrase headline ("Results") tells the audience nothing about what the result actually is. Meanwhile, a wall of bullet text competes directly with your spoken words for the audience's attention — people can't fully read a bullet list and fully listen to you talking at the same time, so one of the two loses. The result is a slide that's simultaneously overwhelming and uninformative.
The assertion-evidence approach
Developed by Penn State's Michael Alley and grounded in multimedia learning research, this approach restructures slides around two elements instead:
- A sentence headline that states the slide's main message — not "Results," but "The new method reduces error by 8% over the baseline." A reader skimming just your headlines, slide by slide, should be able to follow your entire talk's argument.
- Visual evidence supporting that assertion — a graph, diagram, photo, or a small, focused piece of data, rather than a bullet list. The visual does the explaining; you narrate it live, rather than reading text off the slide.
The effect is a deck that's easier for an audience to follow, because the headline gives them the takeaway immediately and the visual reinforces it, instead of asking them to read and listen simultaneously.
Why is this important?
Slides exist to support your spoken talk, not to replace it or compete with it. A slide the audience can fully read in five seconds, paired with you narrating the details live, keeps their attention where it should be — on you and your argument — rather than splitting it between reading and listening.
General slide design principles, beyond assertion-evidence
- One idea per slide. If you find yourself wanting to fit two separate points on one slide, that's usually a sign you need two slides.
- Large, legible text and clean visuals. Assume some audience members are sitting far from the screen; small font sizes and dense diagrams simply won't be readable to them.
- Consistent visual style — fonts, colours, and layout should stay consistent throughout, so the audience isn't distracted by unnecessary variation between slides.
- Don't read your slides aloud word-for-word. If the slide already says everything you're about to say, the audience has no reason to listen to you rather than just reading ahead.
Tips
- Draft your slide headlines first, as a full outline, before building any actual visuals — if the sequence of headlines alone doesn't tell a coherent story, fix that before spending time on graphics.
- Bring your own data and figures rather than defaulting to generic clip art or stock photography — visual evidence drawn from your own work is both more credible and easier for you to speak to fluently.
- Practice speaking to your visual evidence without reading from notes — being able to explain your own graph out loud, unscripted, is a good sign you actually understand it well.
References
Alley, M. (2013). The Craft of Scientific Presentations: Critical Steps to Succeed and Critical Errors to Avoid (2nd ed.). Springer. The book behind the assertion-evidence approach.
Video: Michael Alley — Rethinking Scientific Presentations: The Assertion-Evidence Approach
iBiology — Rethinking Scientific Presentations: Slide Design and Delivery