Survival rates are not the same as mortality rates

Yesterday’s post drew a stronger response than I expected.  Surprisingly, the email I received was about evenly split between people who claimed no one serious ever says “we have the best health care system in the world” and people who claimed “we have the best health care system in the world”.  I wish I could somehow get you all to talk to each other.

Regardless, many of the emails attesting to the superiority of the US health care system proclaimed “Our survival rates for [fill in the cancer] are better!”  And while we can argue whether our ability to extend the life of a relatively small number of people a short period of time is the true hallmark of quality, it’s our fixation on survival rates and not mortality rates that is telling.

Mortality rates define 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 five year survival rate for people with lung cancer in the US is 15.6%.

But here’s the thing.  You can only decrease the mortality rate by preventing death, or curing the disease.  That’s really it.  That’s a cure or a life extension, and both are unequivocally good.  Survival rate, however, can be increased by preventing death, curing the disease, or 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 nine  years to live, with chemo.  From the time you can feel a lump, you have four years to live, with chemo.  Let’s say we have no way to detect the disease until you feel a lump.  The five year survival rate for this cancer is about 0, because within five years of detection, everyone dies, even on therapy.

Now I invent a new scanner that can detect thumb cancer when only one cell is there.  Because it’s the United States, we invest heavily in those scanners.  Early detection is everything, right?  We have protests and lawsuits 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 the treatment.  Everyone is still dying four years after they feel the lump.  But since we are making the diagnosis five years earlier, our five year survival rate is now approaching 100%!  Everyone is living nine years with the disease.  Meanwhile, in England, they say that the scanner doesn’t extend life and won’t pay for it.  Rationing!  That’s why their five year survival rate is still 0%.

The mortality rate is unchanged.  The same number of people are dying every year.  We have 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.

Think this 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 are screened by mammography every year starting at age 40.  For a woman diagnosed with breast cancer in 2001, the five year survival rate in the US was 89.1%; in England it was 80.3%.

The mortality rates?  The American Cancer Society’s Cancer Facts & Figures 2009 reports it’s 25.0 per 100,000 women in the US and Cancer Research UK reports it’s 26.7 per 100,000 women in England.  That’s not as big a difference.  Hard to believe we’re spending almost two and a half times per person for health care what they do over there.

(h/t for some links)

UPDATE: This in no way means I’m opposed to mammography and/or early detection for breast cancer.  But there is a point at which we go overboard.  We need to recognize that and find the sweet spot for screening.  Moreover, that’s not what this post is about.  It’s about cherry picking statistics to make us look better than we are.

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