Aaron: How do we measure our ability to prevent death?  What's the difference between survival and mortality rates?  That's the topic of this week's Healthcare Triage.

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Almost every time someone goes on some "best in the world" rant about the US healthcare system, they inevitably turn to cancer care.  They claim that people in the United States do so much better than those in other countries.  When Rudy Giuliani was running for president, he proclaimed that his chances of surviving his prostate cancer were 82% in the United States, versus only 44% in England under socialized medicine.  Of course, those numbers are completely unsupported by any evidence, if we go by actual data, then the 5-year survival rate of prostate cancer is 98% in the United States versus 74% in England.  Still scary, but pretty irrelevant nonetheless.  I know, I know, some of you are already screaming, how can I dismiss such differences?  I can because they're comparing survival rates, what we really should care about when we compare systems is mortality rates.  I can't stress how important this difference is.  

Mortality rates are defined by the number of people who die of a certain cause in a year divided by the total number of people. For instance, the mortality rate for people with lung cancer in the United States is 53.4 per 100,000 people.  Survival rates are something else entirely, they calculate the percentage of people with a disease who are still alive a set amount of time after diagnosis.  The 5-year survival rate for people with lung cancer in the United States is 15.6%. 53 deaths per 100,000 people and 16%, those aren't measuring the same thing.  

You can only decrease the mortality rate, or the number of people who die each year, by preventing death or curing the disease.  That's really it.  That's a cure or a life extension and both are unequivocally good.  On the other hand, survival rate, or how long you live with a disease, can be increased by preventing death, curing the disease, or by making the diagnosis earlier.  And there's the rub.  

Let's say there's a new cancer of the thumb killing people.  From the time the first cancer cell appears, you have 9 years to live, with or without treatment.  From the time you can feel a lump, you have four years to live, with or without treatment.  Let's say we have no way to detect the disease until you feel the lump.  The five year survival rate for this cancer is about zero, because within five years of detection, everyone dies, even on therapy.  Now I invent a new scanner that can detect thumb cancer at the cellular level.  Because it's the United States, we invest heavily in the technology.  Early detection is everything, right?  We have protests and lawsuits and an awareness campaign with ribbons and everything and now everyone is getting scanned like crazy.  Not only that, but people are getting chemo earlier and earlier for the cancer.  Sure, the side effects are terrible, but we want to live.  We made no improvements to treatment, patients are still dying four years after they feel the lump, but since we're now making the diagnosis five year earliers, our five year survival rate is now approaching 100%.  Everyone's living nine years with the disease.  Meanwhile, in England, they say that the scanner doesn't extend life and they won't pay for it.  Rationing.  That's why their five year survival rate is still 0%.
 
John: USA!  USA!  Yes!  

Aaron: The mortality rate is unchanged, the same number of people are dying every year, we've just moved the time of diagnosis up and subjected people to five more years of side effects and reduced quality of life.  We haven't done any good at all.  We haven't extended life, we've just lengthened the time you have a diagnosis.  We've also spent a crapload of money, but that's almost beside the point.  

You think this thumb cancer scenario is far fetched?  In England, women are screened by mammography every three years starting at age 50, yet in the United States, the American Cancer Society recommends women be screened by mammography every year starting at age 40.  The five year survival rate for a woman diagnosed with breast cancer in 2001 in the US was 89%.  In the UK, it was 80%.  The mortality rates?  In 2010, they were 22 per 100,000 women in the US versus 24 per 100,000 women in the United Kingdom.  That's not as dramatic a difference.  And it's not just women.  We screen way more for prostate cancer, too.  In the US, the ten year survival rate for men with prostate cancer is 98%, for men in the UK, it's 69%.  Huge difference.   But the mortality rate per 100,000 men in the US is 23 versus 23.7 in the UK.  Barely any difference at all.  Hard to believe we're spending almost two and a half times per person for healthcare what they do over there.

Now, that's not to say that survival rates don't have their place.  They do.  Individual doctors need them every day for patient care.  When a patient is sitting in a room with her physician, and she's just learned that she has cancer, the only thing she cares about is "What can I expect?'  She doesn't care about the population or the mortality rate, she wants to know, "What's gonna happen to me?"  And that's where survival rates are necessary.  Doctors want to be able to say to patients with confidence that you have a certain chance of living five years or ten years or more.  We want to know that here in the US based on the way we screen if you're this age and have this cancer and it's at this stage, this is the probability you'll live for five years.  That's what patients want to know, and it's totally reasonable, and that's what survival rates can tell us.  What they can't tell us is if that time is based on earlier diagnosis or better outcomes or both.  They can't tell us if we're necessarily improving outcomes.  That's what I care about as a health services researcher.  That's what you should care about when we discuss the quality in the United States healthcare system, and that's why you should use mortality rates to compare our system to others.

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