Are employees at America's top health insurance companies unhappy? Data shows they may be.

This report originally appeared at Thinknum Media.

As the first month of the new year ends, deadlines for health insurance enrollment draw near. While we can't accurately and fairly rank every health insurance plan across all 50 states, we can look at the "health" of the five largest publicly traded health insurance companies — Aetna ($NYSE:AET), Anthem ($NYSE:ANTM), Cigna ($NYSE:CI), Humana ($NYSE:HUM), and UnitedHealth Group ($NYSE:UNH) — to see which ones are set-up for long-term success when it comes to company culture.

On workplace-review website Glassdoor ($GLASSDOOR), current and former employees submit anonymous reviews that help (or warn) potential applicants who may want to know about the company.

At all of these companies, employees are either choosing to not to talk about the companies they work for, or flood the website within days to report their experiences. That, in turn, has caused some unusual, and somewhat concerning, Glassdoor trends for these five health insurance providers.

Take Aetna, a company with an odd adverse relationship between its Business Outlook — whether employees believe the company's future will be good or bad in six months — and Recommendation ratings.

But, in looking at the company's review count, the number of recent reviews has been dropping significantly over time.

Cigna also faces a similar dilemma; its CEO, David Cordani, has gotten a more positive approval rating over the past year.

At the same time, the number of relevant and recent reviews of him are declining, which, on the surface, seems like a sign of complacency from employees both former and current at the company.

Humana is in the same boat as Cigna and Aetna, with more old reviews being taken out of the ratings equation and no recent reviews coming in to replace them.

Simply put, employees at these three companies are not voicing their opinions — both positive and negative — on their employers through Glassdoor. That's not only concerning for studying employee sentiments at these companies, but also for those looking for a relevant review of the company before they decide to apply for a job there.

The anomalies: UnitedHealth Group and Anthem

While Aetna, Cigna, and Humana all have declining ratings, Anthem has actually bucked the trend thanks to a review surge in July 2018.

This makes ratings for the company, such as with Anthem's Recommendation rating, a more updated metric that can be useful for those considering a job there.

Because the company's recommendation rating rose quickly in July, however, there is some skepticism about the accuracy of Anthem's employee sentiment. As reported by the Wall Street Journal, some companies reportedly manipulate ratings with a dump of positive reviews that causes unusual spikes.

Meanwhile, UnitedHealth Group has a more interesting difference from the pack.

Like the usual trend, UnitedHealth Group had a declining number of reviews as 2018 went on. But then, on one day in January, the number of reviews for the company spiked significantly.

Whether this could be another manipulated spike is yet to be determined, but in either case, UnitedHealth Group and Anthem aren't necessarily healthier than their peers when it comes to Glassdoor ratings.

Want to see the data in this report? Click here.