Over the years I’ve spilled a lot of (metaphorical) ink on how to read science on the internet. At this point almost everyone who encounters me frequently IRL has heard my spiel, and few things give me greater pleasure than hearing someone say “you changed the way I read about science”. While I’ve written quite a fewer longer pieces on the topic, recently I’ve been thinking a lot about what my “quick hits” list would be. If people could only change a few things in the way they read science stories, what would I put on the list?
Recently, a story hit the news about how you might live longer if your doctor is a woman and it got me thinking. As someone who has worked in hospitals for over a decade now, I had a strong reaction to this headline. I have to admit, my mind started whirring ahead of my reading, but I took the chance to observe what questions I ask myself when I need to pump the brakes. Here they are:
- What would you think if the study had said the opposite of what it says? As I admitted up front, when I first heard this study, I reacted. Before I’d even made it to the text of the article I had theories forming. The first thing I did to slow myself down was to think “wait, how would you react if the headline said the opposite? What if the study found that patients of men did better?” When I ran through those thoughts, I realized they were basically the same theories. Well, not the same…more like mirror image, but they led to the same conclusion. That’s when I realized I wasn’t thinking through the study and it’s implications, I was trying to make the study fit what I already believed. I admit this because I used this knowledge to mentally hang a big “PROCEDE WITH CAUTION” sign on the whole topic. To note, it doesn’t matter what my opinion was here, what matters is that it was strong enough to muddy my thoughts.
- Is the study linked to? My first reaction (see #1) kicked in before I had even finished the headline, so unfortunately “is this real” comes second. In my defense, I was already seeing the headlines on NPR and such, but of course that doesn’t always mean there’s a real study. Anyway, in this case of this study, there is a real identified study (with a link!) in JAMA. As a note, even if the study is real, I distrust any news coverage that doesn’t provide a link to the source. In 2017, that’s completely inexcusable.
- Do all the words in the headline mean what you think they mean? Okay, I’ve covered headlines here, but it bears repeating: headlines are a marketing tool. This study appeared under several headlines such as “You Might Live Longer if Your Doctor is a Woman“. What’s important to note here is that by “live longer” they meant “slightly lower 30 day mortality after discharge from the hospital”, by doctor they meant “hospitalist”, and by “you” they meant “people over 65 who have been hospitalized”. Primary care doctors and specialists were not covered by this study.
- What’s the sample size and effect size? Okay, once we have the definitions out of the way, now we can start with the numbers. For this study, the sample size was fantastic….about 1.5 million hospital admissions. The effect size however….not so much. For patients treated by female physicians vs male, the 30 day mortality dropped from 11.49% to 11.07%. That’s not nothing (about a 5% drop), but mathematically speaking it’s really hard to reliably measure effect sizes of under 5% (Corollary #2) even when you have a huge sample size. To their credit, the study authors do include the “number to treat”, and note that you’d have to have 233 patients treated by female physicians over male physicians in order to save one life. That’s a better stat than the one this article tried to use “Put another way – if you were to replace all the male doctors in the study with women, 32,000 fewer people would die a year.” I am going to bet that wouldn’t actually work out that way. Throw “of equal quality” in there next time, okay?
- Is this finding the first of it’s kind? As I covered recently in my series on “Why Most Published Research Findings Are False“, first of their kind exploratory studies are some of the least reliable types of research we have. Even when they have good sample sizes, they should be taken with a massive grain of salt. As a reference, Ioannidis puts the chances that a positive finding is true for a study like this at around 20%. Even if subsequent research proves the hypothesis, it’s likely that the effect size will diminish considerably in subsequent research. For a study that starts off with a 5% effect size, that could be a pretty big hit. It’s not bad to continue researching the question, but drawing conclusions or changing practice over one paper is a dangerous game, especially when the study was observational.
So after all this, do I believe this study? Well, maybe. It’s not implausible that personal characteristics of doctors can effect patient care. It’s also very likely that the more data we have, the more we’ll find associations like this. However, it’s important to remember that proving causality is a long and arduous process, and that reacting to new findings with “well it’s probably more complicated than that” is an answer that’s not often wrong.