Are telephone polls understating support for Trump?

Overall, the survey experiment did not find significant mode differences in overall opinion about Trump or many of his signature policy positions. The web mode yielded estimates that were 1.8 percentage points more supportive of Trump and his policy positions, on average, than estimates from the phone mode.3 The differences ranged from 0 to 8 percentage points. In total, four of the 27 differences observed were statistically significant using conventional testing for opinion polls.4 And not all differences were in the direction one might expect based on the theory that people conceal their support for Trump and his policies in telephone interviews.

The two items that showed the largest difference between web and phone both focused on the policy treatment of undocumented immigrants. On two questions about this issue, web respondents expressed more support for deportation of undocumented immigrants than those interviewed by telephone.

That said, the big picture about where the public stands on Trump’s signature policies is not dependent upon whether the poll was conducted online or by phone. Both modes tell the same story. Both find minority support for a wall along the entire Mexican border, minority support for the travel restrictions on certain majority-Muslim countries, minority support for a national law enforcement effort to deport immigrants living in the U.S. illegally and an essentially even split on attitudes toward the 2010 health care bill.