It’s a symptom of the broken way we pay for medical care.

In the United States, women make less money than men in similar jobs. This is a fact that is really not contested. What is contested, though, is why. Because there’s more to a job than the title.

We aren’t going to untangle the systemic differences in gender pay writ large today, but we can take a pretty deep dive into the discrepancy seen among primary care docs thanks to this study, published in the New England Journal of Medicine.

This is a pretty special analysis, thanks to a level of granular detail that I’ve really never seen before when people have tried to dig into these questions. 

Researchers led by Dr. Ishani Ganguli at Harvard extracted data from Athenahealth, an electronic health record provider.

In total, they pulled over 24 million primary care visits involving more than 8 million patients and 8000 primary care providers across the US.

The cool thing here is that they not only got claims data – how much these physicians billed – but patient characteristics, and – critically – the amount of time the physicians spent with the patients, down to the minute.

Let’s drill down on the data on multiple levels. I think it will tell us something important about how our medical payment system is, well, broken.

OK topline results. In 2017, female PCPs billed 12.4% less than their male colleagues, a difference that averaged around $45,000 less per year. After adjustment for physician age, academic degree, and specialty, female physicians billed 10.9% less per year.

Why?

It wasn’t the patients. Female PCPs, in general, had patients with a greater number of diagnoses and placed more orders for them, so case mix doesn’t really explain this.

The big reason is that female PCPs saw less patients – 10.8% less than their male colleagues.

So – are we done? Easy explanation? Not yet – the plot thickens a bit.

Why did female PCPs see fewer patients?

It’s not because they worked fewer days. They worked just 2.6% fewer days per year.

Even when the team compared billing just on days where PCPs worked, female PCPs billed 10.1% less than their male colleagues.

And female PCPs worked just as many hours as the male PCPs. You can do the math, but what this means is that female PCPs spent more time with their patients than the male PCPs. This is the difference – this is the key to the billing disparity. You can see the right-shift here on this histogram.

Multiple prior studies have shown that more time spent with patients in the primary care setting is associated with better outcomes – more appropriate cancer screening, vaccinations, preventative health, etc. I should note that this particular study did not look at patient outcomes. But still - why do we punish docs who spend more time with their patients?

Female and male PCPs spent the same amount of time on patient care, but the average female PCP billed $398.50 per hour of patient care. Male PCPS? $460.40 per hour.

Some of this disparity could be fixed just through picking different billing codes. When a visit lasts longer, it is eligible for a higher billing code. For example, 15% of female level 3 visits billed by female PCPs could have been eligible for level 4 by time alone, compared to 10% of male PCP visits. 6% of level 4 visits with female PCPs could be billed at level 5 based on time compared to 4% for the male PCPs. Billing for time might help since time spent seems to be the difference here.

But let’s be honest. The real underlying problem here is that our medical payment system rewards volume, not quality. If you want to make more money as a PCP there’s basically one way: see more patients. But doctors, and patients, both want to have more time to see each other. And, as I mentioned, care improves when you have more time.

This system hurts female PCPs more than male PCPs, but honestly it hurts all of us and our patients. Maybe we can solve this particular case of wage disparity with a solution that isn’t a zero-sum game. There are plenty of alternatives to volume-based billing. That a better system would treat physicians more fairly is a clear win win.

This commentary first appeared on medscape.com.