Republicans are more likely to say they want Donald Trump in the White House if they are taking a poll online versus in a live telephone interview. And, if you’re a highly-educated or engaged Republican voter, it turns out that you’re far less likely to tell another human being you want Trump as president.

That’s what we found in a new Morning Consult study, where we aimed to answer a prominent question raised by Trump’s sustained lead in the polls: Does he perform better online than on the phone?

We interviewed 2,397 registered Republicans and Republican-leaning independents over a week in mid-December and varied how they completed the survey to answer this question. Respondents started the survey online, and about one-third continued to answer questions about Trump and other Republican primary candidates online. Another third answered those same questions with a live interviewer on the phone, and the final third answered the questions with an automated voice on the phone, known as interactive voice response (IVR).

Thirty-eight percent of people who answered questions on the internet chose Trump for president, compared with 32 percent who chose him on the phone with a live interviewer and 36 percent who answered questions via an automated voice on the phone. That six point difference was not seen with other candidates between the different polling methods. Ted Cruz, for example, did about 2 points better on live telephone, as did Ben Carson. Jeb Bush had no difference between the methods.

Trump performed even worse on the phone with a live interviewer if the respondent had some college education. Among adults with a bachelor’s degree or postgraduate degree, Trump performs about 10 percentage points better online than via live telephone. And, among adults with some college, Trump performs more than 10 percentage points better online. Conversely, Republicans with a high school education or less favored Trump on the phone over online.

There was also a split between engaged voters—people who say they are very interested in the election, or have previously voted in primaries or midterms—and the general registered voter population. Trump’s advantage in online polls compared with live telephone polling has a spread of eight to nine percentage points among these engaged voters.

What explains Trump’s worse numbers on the phone? One possible explanation is “social desirability bias,” or in other words, people being reluctant to select Trump when talking to another person because they do not believe it will be viewed as a socially acceptable decision. Trump is not the pick of the political pundits, and people intuitively get that.

Of course, that perceived weakness is also a huge part of Trump’s appeal. He is the billionaire who is hated by the elites, the bombastic candidate who breaks out of politico-speak and tells it like it is.

How much this divide matters is hard to gauge. In an election like the Iowa caucus, where delegates vote in secret but are much more closely watched than the average voter, social desirability bias could play a role. But the vast majority of voters make their choice for president in the privacy of a voting booth – a method mimicked most closely by the anonymity of taking a poll on the internet. What this divide does suggest is that some polling may be understating Trump’s actual level of support.

This study was just our first step in understanding this phenomenon and we hope to start a conversation that can lead to a better understanding of the key differences between prominent polling methodologies today.

To view the whole study, you can access it here.