The researchers who engage in this type of work do their absolute best to tease apart these factors. I’m not questioning their intent or their acumen. But even with the best methods available, it’s very, very hard to prove what events cause death and which are correlated with it.

A study published in 2001 asked physicians to review cases of deaths and then rate not only whether they thought a preventable error might have contributed to the end result, but also how likely death might have been in the absence of an error. As with other studies, they found that almost a quarter of hospital deaths might have been at least “partially preventable.” Only 6 percent of deaths were “probably preventable.” But the “inter-rater reliability,” or the amount that reviewers agreed on each case, was low. It’s hard to parse this determination, and even experts disagree on each case.

They also noted that after considering the three-month prognosis and adjusting for the variability of ratings, only 0.5 percent of patients who died would probably have lived at least three months more in good health if care had been optimal. That’s far, far fewer than the numbers cited.

A similar study (in Britain) from 2012 found that while 5 percent of deaths in hospitals may have a more than 50 percent chance of being preventable (lower than these recent studies), more than half occurred with older, sicker patients who were thought to have less than one year of life left to live.

This isn’t to say that these error-associated deaths aren’t sad or meaningful. They are. I can’t say that enough. But the potential harms of hospitals have to be weighed against the potential benefits. People who think that going to a hospital, or even a doctor’s office, carries no risk are fooling themselves. Beyond mistakes that occur, you’re exposing yourself to risk just by being around many sick patients. Further, the sickest patients are likely to have more medical interventions, and therefore more opportunities to have a preventable error occur.

But it’s somewhat sensationalistic to keep coming up with increasing numbers. I’m not sure it’s doing much good. After the publication of the initial report, defenders of the 98,000 number argued that even if the numbers were wrong, bringing attention to this problem would be good in itself.

Unfortunately, research doesn’t necessarily back that up. A 2010 study in The New England Journal of Medicine followed 10 North Carolina hospitals in the 10 years after the Institute of Medicine report. They found that the overall rate of harms, and the rate of preventable harms, did not significantly improve over that period.