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In my last post I introduced some of the controversies surrounding breast (and prostate) cancer screening methods.  I’ve been digging into the research on screening mammography for an assignment for the radiology elective I just finished, and realized there is definitely more on this subject that I want to write about.

 

I’ve been focusing my reading on the perceptions (and misconceptions) about mammography, both on the side of physicians and patients (though breast cancer awareness has become such a public issue, I wish there was research looking at general awareness about cancer, not just awareness in women of screening age- but I digress…).

 

So how effective is mammography?

 

Over the years, quite a lot of data has been generated looking at the ability of screening mammography to prevent death from breast cancer.  I’m not going to dig into all the data now, but I want to mention the most recent Cochrane Review (the “Holy Grail” of Evidence Based Medicine (EBM)) and the 2012 New England Journal of Medicine (NEJM) article that I mentioned in my last post.

 

Here is an excerpt from the 2011 Cochrane Review (emphasis mine):

 

…for every 2000 women invited for screening throughout 10 years, one will have her life prolonged and 10 healthy women, who would not have been diagnosed if there had not been screening, will be treated unnecessarily. Furthermore, more than 200 women will experience important psychological distress for many months because of false positive findings. It is thus not clear whether screening does more good than harm.  [1]

 

And from the NEJM (emphasis mine):

 

Despite substantial increases in the number of cases of early-stage breast cancer detected, screening mammography has only marginally reduced the rate at which women present with advanced cancer. Although it is not certain which women have been affected, the imbalance suggests that there is substantial overdiagnosis, accounting for nearly a third of all newly diagnosed breast cancers, and that screening is having, at best, only a small effect on the rate of death from breast cancer. [2]

 

So the eminent minds in evidence based medicine think that it’s unclear if mammograms do more harm than good?  That certainly isn’t the public message that most of us have heard…

 

Liars, damn liars, and statisticians

 

Part of the difficulty of understanding the benefits (and the risks) of mammography is understanding the statistics.  Unfortunately, despite being taught some basics in medical school, I fear that many med students and physicians aren’t good at interpreting data.  Indeed, a 2009 paper found that the vast majority of ob/gyns couldn’t accurately calculate the positive predictive value of a positive mammogram [3].

 

Even if a physician is statistically literate, data can appear much more or less convincing depending on how it’s presented.  A 2011 article entitled “There is nothing to worry about”: Gynecologists’ counseling on mammography” gives some excellent examples [4]. Working with data published in 1996 from a randomized study conducted in Sweden, they emphasize the difference in absolute risk reduction and relative risk reductions.  In the 1996 study, for every 1000 women that were screened there was a decrease in breast cancer deaths from four to three women in favor of the screened group.  An absolute reduction in breast cancer deaths of 1 woman for 1000 screened does not sound particularly impressive, but the relative statistic of “a 25% decrease in mortality” sounds worthwhile [5]. [It is also worth noting that according to the Cochrane review above, the reduction in breast cancer mortality with screening mammography is actually 1 in 2000, or a 15% decrease in relative mortality or a 0.05% decrease in absolute mortality.]

 

When the data is presented as relative risk reduction and not absolute risk reduction, screening mammography looks a lot more beneficial.  Interestingly, the risks of mammography (those of overdiagnosis and over treatment) are often presented as absolute rather than relative risks, seemingly downplaying the adverse consequences while exaggerating the benefits.

 

It’s not just relative…

 

Other mammography statistics can also be used to skew the perception of benefits.  One statistic that has largely fallen out of favor, because of loud protestation from those calling for a realistic analysis of the benefits of mammography, is “survival statistics”.

 

To understand survival statistics we much first understand “lead time” and “lead time bias”.  Wikipedia does a good job explaining this phenomenon, but for those that don’t want to take the time to click over- I will briefly expand.

 

Imagine a disease that kills a person at 65.  Imagine that the person becomes symptomatic for that disease at 63, but with the use of a screening tool we can detect (but not cure) that disease at 55.  The “diagnosis” is given when the disease is first detected, so the person diagnosed at 63 dies 2 years after diagnosis.  The person whose disease was identified at 55 “survives” for 10 years, which sounds great- except really there is no difference in total life expectancy.  Similarly, if you detect a “disease” that would never kill in the first place you can have stunning survival data…

 

Side note: The cancer that isn’t

 

No one questions that breast cancer kills.  The problem is that “breast cancer” is not a single entity, and some of the things that are classified as breast cancer aren’t even in the same ballpark as the diseases that kill.  Case in point is Ductal Carcinoma in situ (DCIS).  Despite having the word “carcinoma” in its name, calling DCIS “cancer” isn’t really fair, though it can progress to cancer.  Sadly we don’t know when, why, or in whom it will progress to invasive cancer.  However, in the majority of women it just sits there, in situ, and is something the woman dies (or would die, if it were left alone,) with, not from [6].  Including the diagnosis of DCIS in survival statistics further skews an already questionable statistic.

 

Back to stats…
 

Promoting mammography by saying that it increases 5-year survival from 23% to 98% sounds impressive, while the actual reduction in the chance of a woman in her fifties dying from breast cancer over the next ten years only drops from 0.53% to 0.46% with mammography [7].

 

Perception

 

If you’ve made it this far, you (like me) may be becoming underwhelmed with the evidence supporting the regular use of screening mammography (and that’s without starting to consider the financial incentives that might encourage the promotion of early and often mammography…).

 

Unfortunately, if I poll most of my fellow classmates, they will emphatically reply that screening mammography is a good thing. It catches cancers (yes). It saves lives (marginally). It’s highly beneficial (that’s debatable).

 

This sentiment is not unique amongst my classmates.  A recent survey shows that over 80% of responding primary care physicians believe screening mammography to be “very effective” in reducing breast cancer mortality in women aged 50-69 [8]. Another study reported that 54% of responding physicians believe that screening mammography is “very effective” at reducing cancer mortality in women aged 40-49 [9], a population where screening mammography decreases the 10 year risk of dying from breast cancer from 0.35% to 0.3% [7]. In yet another study, none of the 20 gynecologists queried mentioned risks of mammography such as over-diagnosis and over-treatment [4].

 

Sentiments amongst patients are similar. A 2001 study found that only 19% of women surveyed accurately assessed screening efficacy realistically, selecting that screening reduced mortality by about 25% in women over 50 (and again, this number is probably closer to 15% according to the most recent Cochrane report, and is equivalent to 1 less death per 2000 women over ten years).  50% of the women who responded estimate that screening mammography reduced breast cancer mortality by 50-75%.  Not surprisingly, women who believed that screening was effective were more likely to plan to have a mammogram [10].

 

Women’s sentiments towards mammography are shaped by many factors.  Patients, like physicians, are largely influenced by personal experiences.  “Knowing someone who survived” can largely influence personal beliefs, as can the media and statements from celebrities and politicians.  The type of media a woman gets her information from can also largely influence her perspective.  A 2001 paper found that publications aimed towards women with lower education levels published articles that were clearly persuasive or prescriptive for screening mammography, while publications aimed towards more educated women included more balanced and informative messages [11].  Therefore, perhaps it is not surprising that higher levels of education are associated with more realistic expectations of mammography [12].

 

So what’s the Cliff-Notes version

 

Despite what many of us have come to believe, screening mammography is not womankind’s salvation in pink.  Alas, it appears that survival (as in real survival, not a 5 year statistic) is basically unchanged whether women participate in screening mammography or not.  Women that do participate also face the sizable risk of experiencing negative repercussions from mammography: false positives (being told there’s something there when there’s not- this is particularly prevalent in younger populations), over diagnosis, and over treatment.

 

I don’t want to downplay breast cancer.  Breast cancer is real.  Breast cancer is terrible.  Breast cancer kills. But the statistics show that whether women are screened or whether a cancer is caught with diagnostics after a lump is appreciated, population survival is largely unchanged.  Furthermore, women suffer ill consequences from over diagnosis and over treatment from screening mammography.

 

So what should we do?

 

Some of the screening recommendations are heading in the right direction.  While the American College of Gynecologists (ACOG) and the American Cancer Society (ACS) recommend that women initiate annual screenings at the age of 40, the most recent US Preventative Task Force (USPTF) recommendations recommend starting biennial mammograms at 50.

 

Personally, I think the USPTF is heading in the right direction, but I, for one, would like to see a mammography recommendation similar to the recommendations for PSA testing for men given by the American Urology Association as I wrote about in my last post.  We shouldn’t do it in the young (read 40-50), we shouldn’t do it in the old (and instead of “old” we really need to talk about life expectancy), and those patients in the middle need to have a serious talk with their doctor about the risks, benefits, and their personal values.

 

We need personalized medicine.  Instead of a carte blanche recommendation about when to start mammography, we need real discussions about an individual’s risks, their values, and the potential benefits and risks of screening.  Of course- that’s a lot more difficult than handing a prescription for a mammogram to every 40 year old woman who walks through the door, but I think that as doctors, we are up to the challenge. 

 

Of course, doctors aren’t up for the challenge if they’re only given 5 minutes to talk to a patient.  We need to value primary care doctors, and the doctor patient relationship, if we’re going to make strides towards personalized medicine- the question is whether the system is up to that challenge, but that’s a question for another day. 

 

1.            Gotzsche, P.C. and M. Nielsen, Screening for breast cancer with mammography. Cochrane Database Syst Rev, 2011(1).

2.            Bleyer, A. and H.G. Welch, Effect of three decades of screening mammography on breast-cancer incidence. N Engl J Med, 2012. 367(21): p. 1998-2005.

3.            Gigerenzer, G., Making sense of health statistics. Bull World Health Organ, 2009. 87(8): p. 567.

4.            Wegwarth, O. and G. Gigerenzer, “There is nothing to worry about”: gynecologists’ counseling on mammography. Patient Educ Couns, 2011. 84(2): p. 251-6.

5.            Nystrom, L., L.G. Larsson, S. Wall, L.E. Rutqvist, I. Andersson, N. Bjurstam, G. Fagerberg, J. Frisell, and L. Tabar, An overview of the Swedish randomised mammography trials: total mortality pattern and the representivity of the study cohorts. J Med Screen, 1996. 3(2): p. 85-7.

6.            Welch, H.G., S. Woloshin, and L.M. Schwartz, The sea of uncertainty surrounding ductal carcinoma in situ–the price of screening mammography. J Natl Cancer Inst, 2008. 100(4): p. 228-9.

7.            Woloshin, S. and L.M. Schwartz, How a charity oversells mammography. BMJ, 2012. 345: p. e5132.

8.            Yasmeen, S., P.S. Romano, D.J. Tancredi, N.H. Saito, J. Rainwater, and R.L. Kravitz, Screening mammography beliefs and recommendations: a web-based survey of primary care physicians. BMC Health Serv Res, 2012. 12: p. 32.

9.            Meissner, H.I., C.N. Klabunde, P.K. Han, V.B. Benard, and N. Breen, Breast cancer screening beliefs, recommendations and practices: primary care physicians in the United States. Cancer, 2011. 117(14): p. 3101-11.

10.            Chamot, E. and T.V. Perneger, Misconceptions about efficacy of mammography screening: a public health dilemma. J Epidemiol Community Health, 2001. 55(11): p. 799-803.

11.            Dobias, K.S., C.A. Moyer, S.E. McAchran, S.J. Katz, and S.S. Sonnad, Mammography messages in popular media: implications for patient expectations and shared clinical decision-making. Health Expect, 2001. 4(2): p. 127-35.

12.            Domenighetti, G., B. D’Avanzo, M. Egger, F. Berrino, T. Perneger, P. Mosconi, and M. Zwahlen, Women’s perception of the benefits of mammography screening: population-based survey in four countries. Int J Epidemiol, 2003. 32(5): p. 816-21.

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1-year Blogiversary

 

It has officially been one year since I started blogging (1 year and 4 days if you’re being exact).  Starting blogging as I started third year medical school was probably not one of my smartest moves.  Third year medical is tough, mainly by being incredibly demanding of your time and sanity. All the same, I’m really glad that I finally started putting words-to-website and getting some of my thoughts out there for others to read.  Blogging is something I had wanted to do for a while, but wonderful people though they are, I think my parents might have disowned me if I’d started writing a blog before I’d finished writing my thesis!

 

Starting blogging during my clinical years has led to a couple things. First- I haven’t been able to put the requisite time into a number of the topics I originally wanted to write about (though I plan to get to these topics eventually!). Second- I’m surprised by how much I want to write about clinical situations and my general experiences on the floors. Together, this means that my blog is slightly different that I had initially imagined and that I have a long list of potential future blog posts (as well as a folder on my desktop with a significant number of “started posts” that may never see the light of day or the glint of a readers eye).

 

I sincerely want to thank everyone who has joined me over the past year on my blogging journey. I deeply appreciate that you take the time to read my musings. I really enjoy getting comments and I apologize that I sometimes get too caught up to reply to all the thoughtful responses.

 

I also want to thank everyone who has shared my blog and my posts.  I’ve had a couple big days when some rather “big shot” bloggers have shared my posts (most recently Mark Sisson gave me a big bump when he shared my snuggling post in last week’s “Link Love”) but I really appreciate (and am humbled) that readers like my posts enough to share them on facebook and twitter . One of the fun elements of having a blog (at least for those with a significant nerdy streak) is keeping an eye on the statistics generated by your blog host… more on that later!

 

Exciting News…

 

I’m very excited to announce that I have been invited to speak at the 2013 Ancestral Health Symposium this August in Atlanta.  I attended the last year’s conference in Boston, and am excited to be speaking on one of my favorite subjects, lipids and liver, at this year’s event.  Tickets are already on sale for society members and early registration starts for non-members on March 15th. The symposium sold out the last two years, so if you plan to attend make sure you reserve your tickets early!

 

In addition to giving a talk on liver and lipids, I’ll also be heading up a panel of ancestrally minded physicians.  The details are yet to be settled, but with a panel including Dr. Emily Deans (of Evolutionary Psychiatry), Dr. Anastasia Boulais (of Primal Med Ed), Dr. Jacob Egbert, and Dr. Don Wilson, I’m sure there will be some interesting discussion exploring how to use ancestral and evolutionary thinking in a variety of clinical fields including psychiatry, hospitalist practice, physiatry, and ob/gyn respectively.  More details to follow!

 

Fun with Stats…

 

As I mentioned above, one of the joys of having a blog (at least for those of us with a nerdish interest in numbers) is keeping an eye on the blog’s stat page.  In addition to showing me which posts are popular and why, it also shows me the search terms that navigate people to my page.  “Principle Into Practice” is a popular google search that navigate people to my page.  Some of the more obscure ones are a little more puzzling (and amusing).  Here are some favorites:

Help me, I’m dating a medical resident

– “Dating in medical school”, “dating a medical student”… some variation on this theme is one of the more popular phrases that gets people to my blog, no doubt linking them to this post . I’m sure that’s not the kind of dating advice the googlers were looking for- sorry!  As for actually dating a med student? Good luck… the first two years are probably more “dating friendly” as the schedule (at least at my school) is quite flexible, but my experience with third year is that your time is generally spent in the hospital or sleeping.  Date a med student at your own peril- they will undoubtedly want to practice physical exam skills on you and they’re probably a bit short on time for making much of a relationship. Also, if you think dating a medical student is bad, I can only imagine the horror that is “dating a medical intern”. Their schedule makes a med-student’s schedule look like a walk in the park!

Can you burst your appendix by eating a lot of pickles

-Umm… no

Can you get out of the country if you have c difficile

– Actually, a lot of people are walking around with C. diff in their system. Problems arise when you have an overgrowth, at which point you probably can’t be anywhere too far from a toilet… (and you need prompt medical attention)

Victoria Principle nude

-This web-surfer undoubtably went away disappointed…

 

Asparagus therapy and human parasites

also

C. diff and asparagus

-I got nothing…

How to sleep during medical school

– My answer? As much as you can, whenever you can.  Refer back to “dating a medical student” if you’d like.

What speciality [sic] in medicine combines clinical practice and evolutionary theory

– I’m not sure, but if you figure it out, please let me know! (Actually, as I’ve argued before, I think there’s a need for an evolutionary perspective in ALL fields of medicine, though perhaps some have more opportunities for evolutionary thinking than others.)

 

Most search terms guide the seeker to appropriate pages, and I hope that my posts enlighten and entertain.  Many of my favorite posts, some of which are also my most popular posts, can be found here on my “Favorites” page, if you’re ever looking for some interesting posts you might have missed!

 

A final thanks….

 

I said it before; I’ll say it again.  Thank you to everyone who reads, shares, and/or comments on my blog.  It’s been a fun year of blogging and I’m looking forward to more posts, speaking at AHS 2013, and continuing to interact with readers, friends, and those who share an interest in ancestral health and evolutionary medicine… and also those who are curious about dating in med school! 🙂

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