Brendan Nyhan in New York Times’ the Upshot makes a smart case for why media coverage of Hillary Clinton’s favorability ratings fails to tell the whole story. It’s true that in past presidential elections, early favorability polls have not predicted the winner, especially not 16 months before voters fill out their ballots. There’s a key difference, however, for Hillary Clinton: Her gender.

Likeability is a non-negotiable for women political candidates – a staggering 90 percent of voters claim it is very important to like a woman in order to vote for her. But likeability is not the only factor for women – their qualifications are paramount, too.

And here’s why that matters: Qualification is tied to likeability for women. The traits rise and fall together, according to Barbara Lee Family Foundation research. That’s not the case for men, who can earn voters while being unlikeable, and without that unlikeable factor affecting how voters view his credentials to do the job. Women must demonstrate both traits at once.

While we look to past elections for patterns, let’s remember that we are at an unprecedented moment in presidential history. As we analyze the data this election season, we must keep in mind that we’ve never before had two women vying for their party’s nomination for the top job. And the fact remains: It really is different when women run.