Latest / The Copywriting Podcast with Fexingo: Sales Letters, Headlines, and Persuasive Writing / How a Single Underline Lifted Response by 38 Percent
Transcript
- Lucas: You're listening to The Copywriting Podcast with Fexingo. I'm Lucas. Luna: And I'm Luna. Today we're looking at one of the smallest changes you can make to a headline that produced one of the biggest lifts we've seen on this show. Lucas: Right. We've talked about word changes, punctuation changes, even a pencil margin note. But this one is almost invisible. It's the underline. A single line under one word in a headline. Luna: And the test showed a 38 percent lift in response. That's massive for something so subtle. Lucas: The study was run by a direct mail agency back in the late 90s, but the results are still cited in copywriting circles today. They sent two versions of a fundraising letter to a list of 50,000 donors. Luna: What was the headline? Lucas: Control version: 'Help us provide clean water to children in need.' Test version: exactly the same words, but they underlined the word 'clean'. Luna: Just 'clean'? Not bold, not italics, just an underline? Lucas: Just an underline. And the response went from 2.1 percent to 2.9 percent. That's a 38 percent relative lift. The agency estimated it drove an extra one point two million dollars in donations over the campaign. Luna: Why 'clean'? Why not 'children' or 'need'? Lucas: That's the key question. The copywriter who designed the test said they wanted to highlight the specificity of the word. 'Clean water' is more concrete than just 'water'. Underlining it told the reader: pay attention, this word carries meaning. Luna: So it's a way of emphasizing the differentiating detail. Lucas: Exactly. In a sea of fundraising letters, everyone talks about water. But 'clean' is the distinction. It implies the absence of disease, the promise of health. Underlining it made that contrast pop. Luna: I've read some research that says underlining actually mimics the way we highlight text when we're studying. It signals to the brain: this is something to remember. Lucas: There's a 2012 study from the journal Applied Cognitive Psychology that found underlining improves recall by about 10 percent compared to plain text. But the effect is even stronger when only one or two words are underlined. If you underline everything, it becomes noise. Luna: Right, so the scarcity of the underline matters. Lucas: Yes. In the fundraising test, they could have underlined 'clean water' or the whole headline. But they chose one word. That restraint gave the underline power. Luna: How does this translate to digital? Because on the web, underlining usually means a link. Lucas: That's the challenge. On a landing page or an email, if you underline a word, people expect to click it. So you have to be careful. But there are ways around it. You could use bold or a different color for emphasis, but the principle is the same: highlight one word that carries the core benefit. Luna: I've seen some email marketers use underlining in the preheader text or in a call to action button. But they make it non-clickable, so it's just a visual cue. Lucas: That works. Another approach is to underline a word in a testimonial or a statistic. The trust factor goes up because it looks like someone highlighted the most important part for you. Luna: Let's talk about another test. I remember one from the early 2000s, a B2B software company. They underlined the word 'free' in a headline and saw a 22 percent lift in click-through. Lucas: Interesting. But 'free' is already a high-powered word. Underlining it might have over-emphasized it, but the context matters. If the offer is genuinely free, underlining it signals confidence. Luna: What about negative words? Could underlining a word like 'risk' work? Lucas: It can, if you frame it correctly. There's a famous insurance direct mail piece that underlined the word 'avoid' in 'avoid this common mistake'. The response rate went up 18 percent. The underline draws attention to the action you want them to take. Luna: So the underline works best on verbs or adjectives that are unique to your offer. Lucas: Exactly. 'Get', 'save', 'discover' — those are too generic. But 'eliminate', 'restore', 'transform' — those carry specific weight. Underline one of those and you guide the reader's eye. Luna: If today was actually useful to you, the way these episodes stay ad-free is listener support. If you've used one of these techniques in your own copy, or even just enjoyed the deep dive, consider buying me a coffee at buy me a coffee dot com slash fexingo. It takes two minutes and it keeps us independent. Lucas: Yeah, I love that. And it really does make a difference. Every single contribution goes into research and production. So if this show has given you something you've actually used, that link is buy me a coffee dot com slash fexingo. All lowercase. Luna: Alright, back to the underline. One more example I think is worth mentioning: a charity that sent a letter with the headline 'You can save a child's life today.' They underlined 'save'. Response jumped 16 percent. Lucas: 'Save' is a strong verb. It's active, it's emotional, it's specific. Underlining it told the reader: this is the action you can take. It's not abstract. Luna: So the common thread is: underline the word that contains the core promise. Lucas: Right. Don't underline the subject. Don't underline the filler. Underline the one word that, if removed, would change the meaning of the headline. Luna: Let's talk about implementation. If you're writing an email today, how do you decide which word to underline? Lucas: I'd start by writing the headline, then reading it out loud. Which word gets the most natural emphasis when you speak it? That's your candidate. Then test it. Luna: Now, a word of caution: underlining can look dated in some contexts. If your brand is modern and minimal, a single underline might feel like a relic from the 90s. Lucas: That's a fair point. But I think the data says it still works, especially in direct mail and long-form sales pages. On social media, you can't underline anyway, so you have to use other cues like emojis or all-caps. Luna: What about in a PDF or a white paper? Underlining key stats can increase readership. Lucas: Absolutely. In a white paper, underlining a statistic in a pull quote can make it more quotable. It signals to the skimmer: here's the number you need. Luna: There's also the question of underlining in a headline vs. in the body copy. Does it matter where you place it? Lucas: The test we opened with was in the headline. But I've seen tests where underlining a word in the first sentence of the body copy lifted response by 12 percent. The principle is the same: draw attention to the most important idea. Luna: So the underline is a tool, not a trick. It works when it's used with intention. Lucas: Exactly. And that's the takeaway. Small changes, when they align with psychological principles, can produce outsized results. The underline is one of the easiest to implement and test. Luna: Next time you write a headline, ask yourself: what is the one word that holds the promise? Then put a line under it. Lucas: And if you do test it, let us know what happens. We love hearing your results. For now, I'm Lucas. Luna: And I'm Luna. Thanks for listening.