When health officials learned that the 2015 measles outbreak was caused by clusters of unvaccinated children, Americans once more wanted to understand why some parents do not vaccinate their children. In our highly polarized culture, media commentators and even academics began to connect opposition to vaccination to either the left or right of politics.

So a question arises: Who is more likely to be opposed to vaccination, liberals or conservatives? As a sociologist who studies infectious disease, I took a look at this. The answer seems to depend on what question you ask.

Because the outbreak started in the wealthy, liberal enclave of Marin County, California, and because some of the best-known “anti-vaxxers” are Hollywood actors, some right-leaning media outlets connected opposition to vaccination to liberals and related it to other “anti-science” beliefs like fear of GMOs, use of alternative medicine, and even astrology. Other writers have opposed such a caricature and have argued that opposition to vaccination is actually either bipartisan or a specifically conservative problem. Academic research on the topic is also conflicted.

While historians have shown that there is a long history of opposition to vaccination in America, the contemporary anti-vaccination movement got its major boost in 1998 when Andrew Wakefield published faulty research in The Lancet that falsely claimed that the mumps, measles and rubella (MMR) vaccine was related to autism.

As to whether liberals or conservatives are now more likely to be opposed to vaccination, some researchers have suggested that, while anti-vaccination beliefs have spread to libertarians on the right, the anti-vaccination movement originates and finds its strongest support in the political left. A later article by the same researchers similarly argues that Centers for Disease Control and Prevention (CDC) evidence shows that states that voted for Obama in 2012 have higher rates of nonmedical vaccination exemptions.

Yet, other research suggests that it is in fact conservatives who are more likely to believe that vaccines cause autism, that it is liberals who are more likely to endorse pro-vaccination statements and that the more strongly someone identifies with the Republican Party, the more likely he or she is to have a negative opinion of vaccination.

Some new evidence

The Pew Research Center has conducted two surveys that asked about vaccination. One survey in early 2015 asked respondents about whether they thought vaccines were safe, and another survey in late 2014 asked respondents about U.S. vaccination policy and whether vaccination for children should be required or a parent’s choice.

When relating the answers to these questions in the Pew surveys to people’s political views, I find an interesting divergence. The more conservative and also the more liberal someone is, the more likely he or she is to believe that vaccination is unsafe.

Yet only those who are very conservative are more likely to believe that vaccination should be a parent’s choice. This suggests the social dynamics that shape Americans’ personal beliefs about vaccine safety are not the same as the social dynamics that shape their views about whether parents can decide not to vaccinate their children.

To examine this issue, I used a statistical technique called logistic regression that allows you to examine how the probability of a certain outcome will change depending on the characteristics of a survey respondent. I used it to examine whether someone is more or less likely to think that (a) vaccines are unsafe and (b) that vaccination should be a parent’s choice depending on what political beliefs they hold.

I did this while controlling for respondents’ level of education, income, race/ethnicity, age, gender, and parental status. I used the category of “moderates” (what statisticians call a “reference category”) to compare liberals and conservatives with. Let’s first look at people’s personal beliefs about vaccine safety.

What I found is that the more political someone is, the more likely he or she is to believe that vaccines are unsafe. Those who are “very conservative” are one-and-a-half times more likely to believe this than moderates.

Yet, the same is true for those on the left: compared to moderates, those who are very liberal are also one-and-a-half times more likely to believe vaccines are unsafe. It seems that it does not matter what your politics are, the more partisan, the more likely you believe vaccines are harmful.

When we look at whether people think that vaccination should be mandatory or a parent’s choice, a different story emerges.

Now it is only the very conservative who are more likely to think that it should not be mandatory: they are twice as likely as moderates to think that it should be a parent’s choice. Liberals are now more likely to think vaccination should be required: Compared to moderates, liberals are 43.5 percent less likely to think it should be a parent’s choice and those who are very liberal are 14.2 percent less likely.

What explains this divergence? First we have to realize that there is a difference in the overall number of Americans who believe that vaccinations are unsafe versus the number who believe it should be a parent’s choice. The Pew surveys indicate that 8 percent of the U.S. population think that vaccines are unsafe, while 28.2 percent think it should be a parent’s choice.

This suggests that there are a number of people who believe that vaccines are safe but also believe that vaccinations should be a parent’s choice. Why would someone believe that? It may have more to do with their views of the government than their beliefs about vaccines.

Maybe it’s not about vaccines, but about who’s in power

Since President Obama was elected in 2008, those on the right have had a much more negative opinion about the federal government. The 2014 Pew survey shows that those who were dissatisfied with the direction of the country in 2014 were 10 percent more likely to believe vaccination should be a parent’s choice than those who were satisfied (33.3 percent compared to 22.7 percent). Who were the most dissatisfied with the direction of the country in 2014? The very conservative (89.1 percent) and the conservative (81.5 percent).

Essentially, it doesn’t matter if you are conservative or liberal; the more political someone is, the more likely he or she is to think that vaccines are unsafe. Yet it is only the very conservative that are more likely to believe that vaccination should be a parent’s choice.

When it comes to political affiliation, it appears that the social forces that shape Americans’ personal beliefs about vaccination safety are not the same as the social forces that shape their views of U.S. vaccination policy.

Beliefs about U.S. vaccination policy and the role of parents’ choice may have more to do with what Americans believe about the proper role of the government and which political party is in power than what they think about vaccines.

Charles McCoy does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond the academic appointment above.