This article was first published on City A.M.

There are two truisms of election campaigns. The first is they are about the fundamentals: the state of the economy, how long the governing party has been in power, and which party leader is perceived as the more ideologically moderate. For the 2019 General Election we add the fundamental issue of Brexit.

The second is that political campaign messages should be simple. “Keep it simple, stupid” originated in engineering, but is credited with Barack Obama’s 2008 “change” message and Vote Leave’s successful “take back control” campaign in 2016.

It’s now accepted among behavioral scientists that a range of seemingly irrelevant cognitive biases impact important decisions we think we’re making in a rational and reflective manner – such as which party to support in an election. For example, we tend to feel the pain of a loss of something more than the equivalent gain; we’re all a bit too confident in our own abilities; and we’re influenced when making judgements by how readily examples come to mind rather than just facts.

The argument dilution effect is another cognitive bias. This explains that when we’re making judgments based on a lot of information, the details of all that information start to average out. Whether relevant or irrelevant, considering an onslaught of less-relevant details right alongside the fundamental information turns it into white noise.

A study in Nature showed that seeing more medication side effects makes patients evaluate drugs as less harmful. Patients were more likely to favor a drug when its minor side effects, such as risk of headache, were mentioned alongside more major side effects, such as risk of heart attack.

Other studies demonstrate a similar effect in assessing the guilt of suspects on trial and how consumers make judgements about brands. But no one’s studied the argument dilution effect in politics. Should campaigns stick to the simple fundamentals – and what happens when they don’t?

We conducted an experiment with 1,000 voters showing two different groups different tweets by the same politician. Each tweet began with a sentence you might see in a typical politician’s tweet, such as “If reelected, I will bring high quality jobs to our area and ensure that we have the best schools and colleges”. To the tweet one of the groups read, we appended that standard message with a largely irrelevant sentence “I will never be even a minute later to work. I will take turns getting coffee and breakfast for my assistant.”

When it came to qualification, commitment to winning, and likelihood of representing “people like you” each group rated the candidate equally. But the diluted tweet with irrelevant statements about coffee and breakfast made respondents rate the candidate as about 20 percent less likely to win, and they were also less likely to watch or read about the candidate.

This conforms to conventional intuition that voters may be more convinced by shorter messages that stay on the fundamentals.

However, the effects were reversed with similarly appended statements geared at attacking their opponent. One group saw the tweet “My opponent in the upcoming election has no experience in public office and has never served in our Armed Forces,” and the second group saw that with the following added to the end: “He admits to rarely if ever recycling his newspapers and used plastic bottles. He even failed his history exams—twice!”

You’d be excused for expecting the longer diluted attack including struggles with exams to strike the voter as irrelevant and consequently off-putting, and the simpler attack on the fundamentals as more persuasive. But no. The “diluted” message made people think the opponent was about 15 percent less likely to win and an equal percentage less likely to represent “people like you.”

These findings have implications for widely held assumptions about the current campaign. Of course, more study is needed to confirm and expand these findings. But our experiment begs campaign strategists a rethink (not a complete trashing) of the received wisdom.

Long story short, when you’re selling yourself, keep it simple and direct or they won’t think you can win. But when you’re attacking your opponent, a more diluted or “kitchen sink” approach appears to do more damage.