Skip to content
  • About
  • Contact
  • Contribute
  • Book
  • Careers
  • Podcast
  • Recommended
  • Speaking
  • All
  • Physician
  • Practice
  • Policy
  • Finance
  • Conditions
  • .edu
  • Patient
  • Meds
  • Tech
  • Social
  • Video
    • All
    • Physician
    • Practice
    • Policy
    • Finance
    • Conditions
    • .edu
    • Patient
    • Meds
    • Tech
    • Social
    • Video
    • About
    • Contact
    • Contribute
    • Book
    • Careers
    • Podcast
    • Recommended
    • Speaking

Men and women doctors versus correlation and causation

Ashish Jha, MD, MPH
Physician
January 27, 2017
95 Shares
Share
Tweet
Share

Our recent paper on differences in outcomes for Medicare patients cared for by male and female physicians created a stir. While the paper received broad coverage and mostly positive responses, there have also been quite a few critiques. There is no doubt that the study raises questions that need to be aired and discussed openly and honestly. Its limitations — which the paper highlights — are important. Given the temptation we all feel to overgeneralize, we do best when we stick with the data. It’s worth highlighting a few of the more common critiques that have been lobbed at the study to see whether they make sense and how we might move forward. Hopefully, by addressing these more surface-level critiques, we can shift our focus to the important questions raised by this paper.

Correlation is not causation

We all know that correlation is not causation. It’s epidemiology 101. People who carry matches are more likely to get lung cancer. Going to bed with your shoes on is associated with higher likelihood of waking up with a headache. No, matches don’t cause lung cancer any more than sleeping with your shoes on causes headaches. Correlation, not causation. Seems straightforward and it has been a consistent critique of this paper. The argument is that because we had an observational study — that is, not an experiment where we proactively, randomly assigned millions of Americans to male-versus-female doctors — all we have is an association study. To have a causal study, we’d need a randomized, controlled trial. In an ideal world, this would be great, but unfortunately, in the real world, this is impractical and even unnecessary. We often make causal inferences based on observational data — and here’s the kicker: Sometimes, we should. Think smoking and lung cancer. Remember the RCT that assigned people to smoke (versus not) to see if it really caused lung cancer? Me either, because it never happened. So, if you are a strict “correlation is not causation” person who thinks observational data only create hypotheses that need to be tested using RCTs, you should only feel comfortable stating that smoking is associated with lung cancer, but it’s only a hypothesis for which we await an RCT. That’s silly — smoking causes lung cancer.

How can we be so certain that smoking causes lung cancer based on observational data alone? Because there are several good frameworks that help us evaluate whether a correlation is likely to be causal. They include the presence of a dose-response relationship, plausible mechanism, corroborating evidence and absence of alternative explanations, among others. Let’s evaluate these in light of the gender paper. Dose-response relationship? That’s a tough one — we examine self-identified gender as a binary variable (the survey did not ask physicians how manly the men were). So that doesn’t help us either way. Plausible mechanism and corroborating evidence? Actually, there is some here — there are now over a dozen studies that have examined how men and women physicians practice, with reasonable evidence that they practice a little differently. Women tend to be somewhat more evidence-based and communicate more effectively. Given this evidence, it seems pretty reasonable to predict that women physicians may have better outcomes.

The final issue — alternative explanations — has been brought up by nearly every critic. There must be an alternative explanation! There must be confounding! But the critics have mostly failed to come up with what a plausible confounder could be. Remember, a variable, in order to be a confounder, must be correlated both with the predictor (gender) and outcome (mortality). We spent over a year working on this paper, trying to think of confounders that might explain our findings. Every time we came up with something, we tried to account for it in our models. No, our models aren’t perfect. Of course, there could still be confounders that we missed. We are imperfect researchers. But that confounder would have to be big enough to explain about a half a percentage point mortality difference, and that’s not trivial. So I ask the critics to help us identify this missing confounder that explains better outcomes for women physicians.

Statistical versus clinical significance

One more issue warrants a comment. Several critics have brought up the point that statistical significance and clinical significance are not the same things. This too is epidemiology 101. Something can be statistically significant but clinically irrelevant. Is a 0.43 percentage point difference in mortality rate clinically important? This is not a scientific or a statistical question. This is a clinical question. A policy and public health question. And people can reasonably disagree. From a public health point of view, a 0.43 percentage point difference in mortality for Medicare beneficiaries admitted for medical conditions translates into potentially 32,000 additional deaths. You might decide that this is not clinically important. I think it is. It’s a judgment call and we can disagree.

Ours is the first significant national study to look at outcome differences between male and female physicians. I’m sure there will be more. This is one study — and the arc of science is such that no study gets it 100% right. New data will emerge that will refine our estimates and of course, it’s possible that better data may even prove our study wrong. Smarter people than me — or even my very smart co-authors — will find flaws in our study and use empirical data to help us elucidate these issues further, and that will be good. That’s how science progresses: through facts, data and specific critiques. “Correlation is not causation” might be epidemiology 101, but if we get stuck on epidemiology 101, we’d be unsure whether smoking causes lung cancer. We can do better. We should look at the totality of the evidence. We should think about plausibility. And if we choose to reject clear results, such as women internists have better outcomes, we should have concrete and testable alternative hypotheses. That’s what we learn in epidemiology 102.

Ashish Jha is an associate professor of health policy and management, Harvard School of Public Health, Boston, MA.  He blogs at An Ounce of Evidence and can be found on Twitter @ashishkjha.

Image credit: Shutterstock.com

Prev

Why this physician can't be her family's doctor

January 27, 2017 Kevin 3
…
Next

The real danger of maintenance of certification and what to do about it

January 27, 2017 Kevin 12
…

Tagged as: Hospital-Based Medicine

Post navigation

< Previous Post
Why this physician can't be her family's doctor
Next Post >
The real danger of maintenance of certification and what to do about it

More by Ashish Jha, MD, MPH

  • Ranking the world’s health systems: These results may surprise you

    Ashish Jha, MD, MPH
  • How much does it matter which hospital you go to?

    Ashish Jha, MD, MPH
  • The difference between male and female physicians. Here’s what it means.

    Ashish Jha, MD, MPH

Related Posts

  • Can doctors see beyond a patient’s weight?

    Laura Fraser
  • Why do doctors who hate being doctors still practice?

    Kristin Puhl, MD
  • Doctors: It’s time to unionize

    Thomas D. Guastavino, MD
  • Doctors, listen up! You’ll be a patient soon.

    Michele Luckenbaugh
  • Hormone replacement therapy is still linked to cancer

    Martha Rosenberg
  • When doctors are right

    Sophia Zilber

More in Physician

  • Physicians have no autonomy. Here’s how to change that.

    Diane W. Shannon, MD, MPH
  • The erosion of patient care

    Laura de la Torre, MD
  • Navigating adulthood in the digital age

    Eleanor Menzin, MD
  • The power of business knowledge for medical professionals

    Curtis G. Graham, MD
  • Using the language of art to create work-life balance

    Sarah Samaan, MD
  • Lively communication in the service industry

    Deepak Gupta, MD
  • Most Popular

  • Past Week

    • Reigniting after burnout: 3 physician stories

      Kim Downey, PT | Physician
    • Inside the grueling life of a surgery intern

      Randall S. Fong, MD | Physician
    • The erosion of patient care

      Laura de la Torre, MD | Physician
    • I’m tired of being a distracted doctor

      Shiv Rao, MD | Tech
    • Pediatricians grapple with guns in America, from Band-Aids to bullets

      Tasia Isbell, MD, MPH | Policy
    • Doctors and disability insurance: Protecting your income

      Amarish Dave, DO | Finance
  • Past 6 Months

    • Medical gaslighting: a growing challenge in today’s medical landscape

      Tami Burdick | Conditions
    • I want to be a doctor who can provide care for women: What states must I rule out for my medical education?

      Nandini Erodula | Education
    • Balancing opioid medication in chronic pain

      L. Joseph Parker, MD | Conditions
    • I’m a doctor, and I almost died during childbirth

      Bayo Curry-Winchell, MD | Physician
    • Mourning the silent epidemic: the physician suicide crisis and suggestions for change

      Amna Shabbir, MD | Physician
    • Reigniting after burnout: 3 physician stories

      Kim Downey, PT | Physician
  • Recent Posts

    • Doctors and disability insurance: Protecting your income

      Amarish Dave, DO | Finance
    • Emergency care nightmare: the urgent need for experienced nurses

      Rachel Basham, RN, CCRN | Conditions
    • Physicians have no autonomy. Here’s how to change that.

      Diane W. Shannon, MD, MPH | Physician
    • Understanding intersex health care [PODCAST]

      The Podcast by KevinMD | Podcast
    • The erosion of patient care

      Laura de la Torre, MD | Physician
    • Debating the role of psychiatric assessments in medical decisions

      Christian Youssef & Francisco M. Torres, MD | Conditions

Subscribe to KevinMD and never miss a story!

Get free updates delivered free to your inbox.


Find jobs at
Careers by KevinMD.com

Search thousands of physician, PA, NP, and CRNA jobs now.

Learn more

View 4 Comments >

Founded in 2004 by Kevin Pho, MD, KevinMD.com is the web’s leading platform where physicians, advanced practitioners, nurses, medical students, and patients share their insight and tell their stories.

Social

  • Like on Facebook
  • Follow on Twitter
  • Connect on Linkedin
  • Subscribe on Youtube
  • Instagram

CME Spotlights

From MedPage Today

Latest News

  • Spine Surgery Cover-Up? Legal Threats Chill Misinfo Research; The Longevity Industry
  • Upcoming Studies on Dupilumab for Alopecia Areata
  • Early Win for PTSD Drug; FDA OKs AI Sleep Diagnostic; Extreme Social Isolation Tool
  • Doctor or DNP: Who Is Really Providing Care?
  • Who Really Needs a Yearly COVID Booster?

Meeting Coverage

  • New Schizophrenia Treatments Are Coming: Don't Panic
  • Loneliness Needs to Be Treated Like Any Other Health Condition, Researcher Suggests
  • Stopping Medical Misinformation Requires Early Detection
  • AI Has an Image Problem in Healthcare, Expert Says
  • Want Better Health Outcomes? Check Out What Other Countries Do
  • Most Popular

  • Past Week

    • Reigniting after burnout: 3 physician stories

      Kim Downey, PT | Physician
    • Inside the grueling life of a surgery intern

      Randall S. Fong, MD | Physician
    • The erosion of patient care

      Laura de la Torre, MD | Physician
    • I’m tired of being a distracted doctor

      Shiv Rao, MD | Tech
    • Pediatricians grapple with guns in America, from Band-Aids to bullets

      Tasia Isbell, MD, MPH | Policy
    • Doctors and disability insurance: Protecting your income

      Amarish Dave, DO | Finance
  • Past 6 Months

    • Medical gaslighting: a growing challenge in today’s medical landscape

      Tami Burdick | Conditions
    • I want to be a doctor who can provide care for women: What states must I rule out for my medical education?

      Nandini Erodula | Education
    • Balancing opioid medication in chronic pain

      L. Joseph Parker, MD | Conditions
    • I’m a doctor, and I almost died during childbirth

      Bayo Curry-Winchell, MD | Physician
    • Mourning the silent epidemic: the physician suicide crisis and suggestions for change

      Amna Shabbir, MD | Physician
    • Reigniting after burnout: 3 physician stories

      Kim Downey, PT | Physician
  • Recent Posts

    • Doctors and disability insurance: Protecting your income

      Amarish Dave, DO | Finance
    • Emergency care nightmare: the urgent need for experienced nurses

      Rachel Basham, RN, CCRN | Conditions
    • Physicians have no autonomy. Here’s how to change that.

      Diane W. Shannon, MD, MPH | Physician
    • Understanding intersex health care [PODCAST]

      The Podcast by KevinMD | Podcast
    • The erosion of patient care

      Laura de la Torre, MD | Physician
    • Debating the role of psychiatric assessments in medical decisions

      Christian Youssef & Francisco M. Torres, MD | Conditions

MedPage Today Professional

An Everyday Health Property Medpage Today
  • Terms of Use | Disclaimer
  • Privacy Policy
  • DMCA Policy
All Content © KevinMD, LLC
Site by Outthink Group

Men and women doctors versus correlation and causation
4 comments

Comments are moderated before they are published. Please read the comment policy.

Loading Comments...