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The pump on Broad Street: Introduction to Evidence Based Medicine PART1



It was another shivering-cold, windy day of autumn 1971.

The hospital room, mystically disguised in cigarette smoke, was full of busy consultants, chest x-rays and illegible scribbles of patients notes from yesterday’s ward rounds, pinned together in clumsy folders. Lively discussion sharply ceased when dr Archie Cochrane entered the room, carrying, to the dismay of his colleagues, another file of tables and figures. His randomised controlled trial of patients treated at Coronary Cardiac Units vs patients released home showed a slight numerical advantage for those who had been discharged.

In it was his randomised controlled trial, a comparison of patients treated at Coronary Cardiac Units with patients released home, showing a slight numerical advantage for those who had been discharged.

Little did they know that he’d wickedly compiled two reports: one reversing the number of deaths on the two sides of the trial and one containing real figures.

The sun was setting down in the windows, but the dim afternoon light was enough for the cardiologists to flick through the results. The already damp atmosphere in the room was so dense, you could hang an axe in the air. The eyes of the consultants pinned down on Archie, with an inevitable slide of judgement crucifying his efforts. In a second, their anger, abuse and outrage were unleashed in a vociferous manner:

Archie,” they said

We always thought you were unethical. You must stop this trial at once!

A fierce contempt and condemnation of Cochrane’s science ensued with full power. They had been objecting to his evidence-based approach for a long time now, and here it was, the final proof! Harming the patients in such a way was an undignifying and appalling offence, not worthy of a fellow human being.

Despite the rampaging fire of criticism, Archie was observing the situation with unusual composure. He let them have their say for a couple of minutes.

I deeply apologise, he said, interrupting the vivid discussion of cardiologists I have not given you the true results, he uttered and showed the real set of figures hidden in his folder.

“I would imagine, dear colleagues, that you will now say, vehemently, that the Coronary Care Units should be stopped immediately,” he concluded looking at terrified faces of the consultants.

There it was: a blunt, dead silence, interrupted only by slight spells of rain hitting the hospital windows. Archie didn’t feel proud, however. He felt rather sick and disgusted. Alas, after all, they were his medical colleagues.

adapted & fictionalised from: Archie Cochrane [1989] One Man’s Medicine (with Max Blythe), BMJ London UK


Of course, today’s coronary care units are quite different than their 1971 equivalents. After 42 years of that remarkable event, we see how evidence can help patients and change their lives by challenging the common sense and clinical experience. I can’t help but smile with pride and unravelled satisfaction each time I hear “What’s the evidence for that?,” being uttered by doctors on the wards. Today, we have an unprecedented access to thousands of datasets, we can view years of people’s lives, diseases, experiences and outcomes, neatly put in a set of spreadsheets and tables, with a power to infer key conclusions and recommendations to save lives of thousands to come.


Why would I want to learn it?

I believe that the Evidence-Based Medicine is one of the greatest inventions of the 20th century and that its advent in medical practice was a revolutionary breakthrough comparable to the discovery of antibiotics or X-rays. It is extremely important for the doctors to feel confident in using this powerful tool in their day-to-day practice, but it is equally important for the patients, scientists, policy makers and voters to know how the evidence is collected, processed and presented, so that they can make informed decisions.



How to:

  • Design a trial to check whether your idea, drug or new treatment is effective
  • Critically evaluate other papers, clinical trials and statistics
  • Spot common tricks and lies people say about results and figures
  • Check if what a doctor/politician/scientist say about the results is true

In a nutshell, you’ll be smarter than half of the GPs practising in the UK.


But what if do not want to be a doctor or a scientist?

Well, at least once in your lifetime, you’ll be deciding on who to vote for, you’ll have to make a decision in a referendum or will be involved in care or treatment of your relative.

Imagine how more confident you’ll be, equipped with a knowledge of statistics, trials and studies, with a power to critically evaluate what people are saying, filter through a noise of headlines and politicians throwing random figures at one another, and be able to get the best information to make a most informed decision about the future of your country, you local community or your own medical treatment.

During this course, I will try to keep the statistics and maths to the minimum, I’ll take you through a journey of different trials and show you how we fight every day for the evidence to be released (and it’s not an easy battle!) and sparkle your learning with lots of interesting real life examples and anecdotes.

Please, do not be discouraged it you can’t understand it all. Immerse yourself in the course and try to understand the take-home message of each lesson. You’ll see that it all will start to make more sense as you go through. If you can’t get your head around something: ignore it and move on.

Ready to go? Make yourself a good cup of tea and let’s begin!


I’ll be using a couple of terms in this course, so just to make sure we’re on the same page:



The conscientious, explicit and judicious use of current best evidence in making decisions about the care of individual patients

Sackett and colleagues (1997)

I couldn’t describe it better: EBM is a science of using the best evidence currently available to make the most optimal decision. It’s not about what we think is best, and it doesn’t have to be logical or explainable. It just is. I’ll talk about it in more detail later on.


This is the science of how health-related issues (e.g. disease) are spread and what determines their distribution in specified population (e.g. a city, country, etc.), with an intention to apply this knowledge to control various health problems.


This will help us display the data appropriately and make it (relatively) easy to read and interpret. It will also study different measures of association and control for human error, like pattern-seeking or chance. The ancient Greeks thought that chance is the power of gods. Statistics is what a mortal human has developed to control the chance and to overcome itself in the fallacy of finding patterns everywhere. So think of it like seizing the God-like power of the mechanisms of nature. Cool, isn’t it?


OK, now let’s have a look at some real-life examples.


Cholera is an infectious disease spread by bacterium Vibro cholerae. In June 1853, there was a cholera outbreak in Soho, a district of London. At the time, the theory of germs wasn’t known, so people didn’t realise disease are spread by small organisms. A local doctor, John Snow conducted a study, putting all incidents of cholera on a map below (black dots). The local water pumps (A) (B) and (C) are marked in orange on this map.

Now, have a look at this copy of the original Snow’s map and answer the questions below.


source: Snow, J. [1855] On the Mode of Communication of Cholera, 2nd Ed, John Churchill, New Burlington Street, London, UK, 1855.

Click here to see the first option


At that time, John Snow argued for the pump handle to be removed, claiming that the water from the pump is the cause of problems. He later came to examine the water supply to this area.


adapted from: Snow J. [1855] On the Mode of Communication of Cholera, London UK 

Around that time, the Lambeth Water Works moved their water supply upstream Thames, where the water was free from London sewages.

Consider the death rate from cholera in Southwark Water Works supply area (110) and compare it to Lambeth Water Works (25), (38).

Click here to see the first option

Well done! You’ve cracked your first epidemiology case! As a bonus question, why do you think the building marked in red was free from deaths? Tweet me @MaxBrzezicki with your answer (don’t look it up, it’s cheating!).

Finally, before we go, consider this example:


Imagine you were an epidemiologist in London at that time. After publishing your study, a local politician claims your figures are incorrect.

“Pointing to the good company of Soutwark Water Works as a cause of cholera outbreak is indeed appalling!!! This company has supplied our water for years, and now you say there’s something wrong with it? Closing the water supply, as you have suggested would mean loss of thousands of jobs! I will not let our good, hard working people of this company to be shamed by your paper. I have conducted a study on my own! People living in Lambeth are more than 9 times more likely to get cholera than those living in Christchurch [Deaths from Cholera in Lambeth (337) / Deaths from Cholera in Christchurch (35) = 9.63]. Yet both these areas are supplied by Lambeth Water Works! So it really doesn’t make any difference, does it? Why don’t you close that down?”

Click here to see the first option


OK – that’s all for this part of the course. Well done for getting this far. I hope you liked it. Please let me know on Twitter if you have any comments, ideas concerns or expectations!


Slicing through the population: Cross-sectional studies.


About the author

Max Brzezicki

Max Brzezicki

Passionate about evidence-based medicine and science, likes slicing meat, crushing rat brains, criminal & public law, foreign languages, rhetoric, history, classical studies and political thought. FNS since 2015.

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