Yesterday I worked on a little data science project reanalyzing the data that made Dr. Ignaz Semmelweis discover the importance of hand-washing. But let’s get back to history for a while. In the early 1840s at the Vienna General Hospital as many as 10% of the women giving birth died from childbed fever. He knew the cause of childbed fever: It’s the contaminated hands of the doctors delivering the babies. And they wouldn’t listen to him and wash their hands!
The table below shows the number of women giving birth at the two clinics at the Vienna General Hospital for the years 1841 to 1846. You’ll notice that giving birth was very dangerous; an alarming number of women died as the result of childbirth, most of them from childbed fever.
We see this more clearly if we look at the proportion of deaths out of the number of women giving birth at Clinic 1.
If we now plot the proportion of deaths at both clinic 1 and clinic 2 we’ll see a curious pattern… and huge problem
Why is the proportion of deaths constantly so much higher in Clinic 1? Semmelweis saw the same pattern and was puzzled and distressed. The only difference between the clinics was that many medical students served at Clinic 1, while mostly midwife students served at Clinic 2. While the midwives only tended to the women giving birth, the medical students also spent time in the autopsy rooms examining corpses.
Semmelweis started to suspect that something on the corpses, spread from the hands of the medical students, caused childbed fever. So in a desperate attempt to stop the high mortality rates, he decreed: Wash your hands! This was an unorthodox and controversial request, nobody in Vienna knew about bacteria at this point in time.
Starting from the summer of 1847 the proportion of deaths is drastically reduced and, yes, this was when Semmelweis made handwashing obligatory.
The effect of handwashing is made even more clear if we highlight this in the graph.
It reduced the proportion of deaths by around 8 percentage points! From 10% on average to just 2% (which is still a high number by modern standards).
All in all, it would seem that Semmelweis had solid evidence that handwashing was a simple but highly effective procedure that could save many lives.
The tragedy is that, despite the evidence, Semmelweis’ theory — that childbed fever was caused by some “substance” (what we today know as bacteria) from autopsy room corpses — was ridiculed by contemporary scientists. The medical community largely rejected his discovery and in 1849 he was forced to leave the Vienna General Hospital for good.
One reason for this was that statistics and statistical arguments were uncommon in medical science in the 1800s. Semmelweis only published his data as long tables of raw data, but he didn’t show any graphs nor confidence intervals. If he would have had access to the analysis like one’s above he might have been more successful in getting the Viennese doctors to wash their hands. That’s the power of statistics in action.