Good. Bad. Stupid. When it comes to his choice of words, Donald Trump keeps it simple.So simple, in fact, that even a nine-year-old can get what the outspoken Republican White House hopeful is saying.

That’s according to a test developed for the US Navy that assesses the complexity of an English text by looking at sentence length and counting syllables.

When this Flesch-Kincaid method is applied to the opening and closing statements made during the last Republican debate, the GOP frontrunner takes the cake for poorest vocabulary among the nine contenders who faced off in Las Vegas on December 15.

It reveals that a mere seven per cent of the words used by Mr Trump in a minute and a half had more than three syllables, meaning that even children as young as nine or 10 would have been able to understand him.

Mr Trump caused astonishment this week by appearing to coin an obscene neologism — “schlonged,” derived from a Yiddish term for penis — to disparage his Democrat rival Hillary Clinton.

But the billionaire businessman typically favours basic, brief words such as “good,” “bad” and “great” for getting his point across on the campaign trail.

“If I’m elected President, we will win again. We will win a lot. And we’re going to have a great, great country, greater than ever before,” Mr Trump promised at the end of the debate.

The tycoon sums up his foreign policy in equally simple terms, for instance describing Syrian President Bashar al-Assad as a “bad guy, very bad guy.”

“Donald Trump tries to reassure his audience by appealing to our elementary political instinct,” said Peter Lawler, a political science professor at Berry College and author of a book on American political rhetoric. “He uses simple, repetitive words,” he told AFP.

“Some part of the population associates simplicity in rhetoric to honesty,” added Matthew Baum, a communications professor at Harvard University’s John F. Kennedy School of Government. “They think that elaborate speeches are too deceptive.”

The 69-year-old tycoon often employs the term “stupid” to describe his rivals and the current government. “We are being run by stupid people. I used to say incompetent. But stupid is really, you know, is the next stage,” he said earlier in December.