Cubans gave the U.S. president a higher approval rating than the Castro brothers. (Post Graphics)

Polls measure President Obama's approval rating every single day, but such ratings are far less common in authoritarian nations due to restrictions on research or the press. Cuba is a polling black hole, where our search found only a single poll in the past decade testing Raul Castro's popularity, and this was conducted by an anti-Castro group.

Filling that void, a new survey by television networks Univision and Fusion and conducted without government authorization asked residents of Cuba to rate both Castro brothers on a scale from "very positive" to "very negative."

[READ: How the Cuba poll was conducted | See full results from the poll]

Cubans gave Raul a split rating of 47 percent positive and 48 percent negative, while Fidel fared slightly worse with a 44-50 positive negative margin.

The poll finds Raul Castro's popularity ranges across a number of demographic groups. He is most popular among the oldest Cuban residents, with 55 percent of those age 65 and older rating him positively. The current president also fares relatively well among those employed by the government, Catholics and people living in the western region, which encompasses Havana.

He is less popular among younger Cubans - 43 percent are positive - as well as among those who identify their religion as Santeria (34 percent) and people living in the central region of the country (37 percent). Castro also receives particularly negative ratings from private sector workers - 55 percent negative.

Fidel's image ranges in similar ways across demographic groups, with higher ratings from government employees and those in the Havana region. He is particularly disliked among those whose religion is Santeria - 69 percent negative.

When surveys ask about leaders in countries with major restrictions on free speech, there is always a concern that respondents may give answers that they think are politically safe. For instance, if they are worried about their individual answers being given to the government, they may refrain from offering negative opinions of political leaders for fear of retribution.

In this study, interviewers made efforts to present the survey as an independent research effort and assure respondents that their answers would remain anonymous. Researchers at Bendixen & Amandi of Miami, Fla, who conducted the survey, reported that interviewers found respondents generally willing to express their views. This was also evidenced by the large number of respondents willing to offer negative appraisals of political leaders.  Read more about how the survey was conducted here.

Read more:

Poll shows vast majority of Cubans welcome closer ties with U.S. 

Cuban millennials restless for opportunity at home or abroad

Interactive results from Univision/Fusion Cuba poll

Surveying Cubans under the Castro Government