Screenshot assertion-evidence website

Use assertion-evidence web slides for persuasion

Screenshot assertion-evidence website

Looking to build a case on your web page? To persuade an audience to take an action? Take a cue from some fascinating research about assertion-evidence presentation slide design.

You’ve probably sat through as many godawful PowerPoint presentations as I have. Whoever designed the original templates is the culprit. They made it way too easy to throw an outline on a screen, give it a blue background with a couple of swooshes and voila! Presentation complete.


Beginning with a series of scholarly articles in the journal Technical Communication, Professor Michael Alley and colleagues advocate building presentation slides with what they call the “assertion-evidence” method. Rather than hide the point of slide in a cognitive-overload jumble of bulleted text, put a full-sentence assertion at the top of each slide and visual evidence or support underneath.

Students who viewed course content presented as assertion-evidence slides scored higher than those who viewed typical bullet-list slides. Bonus: presenters who created assertion-evidence slides understood and retained the content better too.

From PowerPoint slides to web slides

Check out this page from Tuft & Needle. It’s a great example of vertical web slides, each comprising an assertion (for example, “A mattress shouldn’t cost a fortune”) and skillfully produced visual evidence with a bit of movement. And then some big call-to-action buttons at the bottom of the page.

It works for the same reason as Professor Alley’s PowerPoint slides: It makes its case the way we do naturally. We don’t try to persuade somebody by talking in subheads and bullet points. We use full sentences to make assertions; we provide evidence as needed to lead someone to the conclusion we want.

Also like Alley’s PowerPoint style, the Tuft & Needle page moves from one slide to the next. It just moves vertically rather than from screen-to-screen.

The power of narrative

The page also tells a great story. It sets the scene masterfully—”Over-priced, over-complicated mattresses have been the standard. Until now.” It clearly establishes the antagonist (“mattress stores”) and protagonist (“us”). It leads us through the plot—the methods T&F uses to get from the awful, evil current state created by those other mattress stores to the idealized future state possible with a T&F mattress, which you can click to buy at the bottom of the page. Brilliant.

Try it the next time you’re making a page seeking to persuade an audience to buy something, give something, sign-up for something. See if you don’t experience an uptick in conversion rates similar to Professor Alley’s uptick in student retention rates.

And yes, I bought a Tuft & Needle mattress for my daughter. It’s awesome.


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