Donald Trump has wrongly claimed he won "EVERY debate" against Hillary Clinton, despite polls and focus groups indicating he lost all three.

"As most people are aware, according to the Polls, I won EVERY debate, including the three with Crooked Hillary Clinton, despite the fact that in the first debate, they modulated the sound on me, and got caught," the president wrote on Twitter. "This crew looks somewhat easier than Crooked, but you never know?"

But after the final debate of the three, for instance, polling from YouGov showed that voters believed Ms Clinton had performed better than Mr Trump. Data released in 2016 showed Hillary Clinton won against Donald Trump by 49 per cent to 39 per cent, with 12 per cent declaring it a tie, after interviews of 1503 registered voters.

Similar results were seen across the three debates, and in data provided by a variety of different polling companies.

At least some focus groups indicated that Ms Clinton had outperformed Mr Trump. Republican pollster Frank Luntz posted that his post-debate focus group had showed a win for Ms Clinton.

Mr Trump made similar claims at the time of the debates, and was shown to be distorting polling data then. After the second debate, for instance, he posted on Twitter that he had won "the second debate in a landslide (every poll)" – but all of the post-debate polling from major organisations showed that Ms Clinton had won.

At that time, Mr Trump was repeatedly criticised by fact-checkers for making erroneous claims about his performance in the debate.

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While some more informal, online polling at the time had shown victories for Mr Trump, the results of such votes can be heavily skewed by the demographics voting in them. Some Trump-supporting websites ran surveys that showed him winning by a landslide, for instance, but conflicted with polls conducted in a more scientific manner.

Polling throughout the election period had showed Ms Clinton beating Mr Trump right up until the final vote, with the result being widely described as a shock that confounded much of the polling that preceded it.

It is not clear what Mr Trump means in his reference to the sound being "modulated" in the first of his debates with Hillary Clinton. But he appears to be referencing problems with his microphone that meant his voice was more quiet in the hall.