#FOAMPubMed 1: Lemons and Limes, the first clinical trial and how to make a research question


Before we conduct any research we first need to construct a research question. This can be a difficult step. Our question needs to be precise and easy to understand. To do this we can use the ‘PICO’ criteria:


We need a population of interest. These will be subjects who share particular demographics and needs to be clearly documented.


The intervention is something you’re going to do to your population. This could be treatment or education or an exposure such as asbestos. The effect of the intervention is what you’re interested in.


If we’re going to study an intervention we need to compare it. We can use people without the exposure (control) or compare the treatment to another or placebo.


The outcome is essentially what we are going to measure in our study. This could be mortality, it could be an observation such as blood pressure or a statistic such as length of stay in hospital. Whatever it is we need be very clear that this our main outcome, otherwise known as our primary outcome. The outcome decides our sample size so has be explicit.

PICO therefore allows us to form a research question.

To demonstrate this let’s look at the first ever clinical trial and see how we use PICO to write a research question.

It’s the 18th century. An age of empires, war and exploration. Britain, an island nation in competition with its neighbours for hegemony, relies heavily on her navy as the basis of her expansion and conquest. This is the time of Rule Britannia. Yet Britain, as with all sea going nations, was riddled with one scourge amongst its sailors: scurvy.

Scurvy is a disease caused by a lack of Vitamin C. Vitamin C, or ascorbic acid, is essential in the body to help catalyse a variety of different functions including making collagen, a protein which forms the building blocks of connective tissue, and wound healing. A lack of Vitamin C therefore causes a breakdown of connective tissue as well as impaired healing; this is scurvy, a disease marked by skin changes, bleeding, loss of teeth and lethargy. Hardly the state you want your military to be when you’re trying to rule the waves.

James Lind was born in Edinburgh in 1716. In 1731, he registered as an apprentice at the College of Surgeons in Edinburgh and in 1739 became a surgeon's mate, seeing service in the Mediterranean, Guinea and the West Indies, as well as the English Channel. In 1747, whilst serving on HMS Salisbury he decided to study scurvy and a potential cure.

James Lind 1716-1794

James Lind 1716-1794

Lind, as with medical opinion at the time, believed that scurvy was caused by a lack of acid in the body which made the body rot or putrefy. He therefore sought to treat sailors suffering with scurvy with a variety of acidic substances to see which was the best treatment. He took 12 sailors with scurvy and divided them into six pairs. One pair were given cider on top of their normal rations, another sea water, another vinegar, another sulphuric acid, another a mix of spicy paste and barley with another pair receiving two oranges and one lemon (citrus fruits containing citric acid).

Although they ran out of fruit after five days by that point one of the pair receiving citrus fruits had returned to active duty whilst the other was nearly recovered. Lind published his findings in his 1753 work, A treatise on scurvy. Despite this outcome Lind himself and the wider medical community did not recommend citrus fruits to be given to sailors. This was partly due to the impossibility of keeping fresh fruit on a long voyage and the belief that other easier to store acids could cure the disease. Lind recommended a condensed juice called ‘rob’ which was made by boiling fruit juice. Boiling destroys vitamin C and so subsequent research using ‘rob’ showed no benefit. Captain James Cook managed to circumnavigate the globe without any loss of life to scurvy. This is likely due to his regular replenishment of fresh food along the way as well as the rations of sauerkraut he provided.

It wasn’t until 1794, the year that Lind died, that senior officers on board the HMS Suffolk overruled the medical establishment and insisted on lemon juice being provided on their twenty three week voyage to India to mix with the sailors’ grog. The lemon juice worked. The organisation responsible for the health of the Navy, the Sick and Hurt Board, recommended that lemon juice be included on all voyages in the future.

Although his initial assumption was wrong, that scurvy was due to a lack of acid and it was the acidic quality of citrus fruits that was the solution, James Lind had performed what is now recognised as the world’s first clinical trial. Using PICO we can construct Lind’s research question.


Sailors in the Royal Navy with scurvy


Giving sailors citrus fruits on top of their normal rations


Seawater, vinegar, spicy paste and barley water, sulphuric acid and cider


Patient recovering from scurvy to return to active duty

So James Lind’s research question would be:

Are citrus fruits better than seawater, vinegar, spicy paste and barley water, sulphuric acid and cider at treating sailors in the Royal Navy with scurvy so they can recover and return to active duty?

After HMS Suffolk arrived in India without scurvy the Naval establishment began to give citrus fruits in the form of juice to all sailors. This arguably helped swing superiority the way of the British as health amongst sailors improved. It became common for citrus fruits to be planted across Empires by the Imperial countries in order to help their ships stop off and replenish. The British planted a particularly large stock in Hawaii. Whilst lemon juice was originally used the British soon switched to lime juice. Hence the nickname, ‘limey’.

A factor which had made the cause of scurvy hard to find was the fact that most animals can actually make their own Vitamin C, unlike humans, and so don’t get scurvy. A team in 1907 was studying beriberi, a disease caused by the lack of Thiamine (Vitamin B1), in sailors by giving guinea pigs their diet of grains. Guinea pigs by chance also don’t synthesise Vitamin C and so the team were surprised when rather then develop beriberi they developed scurvy. In 1912 Vitamin C was identified. In 1928 it was isolated and by 1933 it was being synthesised. It was given the name ascorbic (against scurvy) acid.

James Lind didn’t know it but he had effectively invented the clinical trial. He had a hunch. He tested it against comparisons. He had a clear outcome. As rudimentary as it was this is still the model we use today. Whenever we come up with a research question we are following the tradition of a ship’s surgeon and his citrus fruit.

Thanks for reading.

- Jamie

Bullet Holes & Bias: The Story of Abraham Wald

“History is written by the victors”

Sir Winston Churchill

It is some achievement if we can be acknowledged as succeeding in our field of work. If that field of work happens to be helping to win the most bloody conflict in history then our achievement deserves legendary status. What then do you say of a man who not only succeeded in his field and helped the Allies win the Second World War but whose work continues to resonate throughout life today? Abraham Wald was a statistician whose unique insight echoes in areas as diverse as clinical research, finance and the modern celebrity obsession. This is his story and the story of survivorship bias. This is the story of why we must take a step back and think.

Abraham Wald and Bullet Holes in Planes

Wald was born in 1902 in the then Austria-Hungarian empire. After graduating in Mathematics he lectured in Economics in Vienna. As a Jew following the Anschluss between Nazi Germany and Austria in 1938 Wald and his family faced persecution and so they emigrated to the USA after he was offered a university position at Yale. During World War Two Wald was a member of the Statistical Research Group (SRG) as the US tried to approach military problems with research methodology.

One problem the US military faced was how to reduce aircraft casualties. They researched the damage received to their planes returning from conflict. By mapping out damage they found their planes were receiving most bullet holes to the wings and tail. The engine was spared.


Abraham Wald

The US military’s conclusion was simple: the wings and tail are obviously vulnerable to receiving bullets. We need to increase armour to these areas. Wald stepped in. His conclusion was surprising: don’t armour the wings and tail. Armour the engine.

Wald’s insight and reasoning was based on understanding what we now call survivorship bias. Bias is any factor in the research process which skews the results. Survivorship bias describes the error of looking only at subjects who’ve reached a certain point without considering the (often invisible) subjects who haven’t. In the case of the US military they were only studying the planes which had returned to base following conflict i.e. the survivors. In other words what their diagram of bullet holes actually showed was the areas their planes could sustain damage and still be able to fly and bring their pilots home.

No matter what you’re studying if you’re only looking at the results you want and not the whole then you’re subject to survivorship bias.

No matter what you’re studying if you’re only looking at the results you want and not the whole then you’re subject to survivorship bias.

Wald surmised that it was actually the engines which were vulnerable: if these were hit the plane and its pilot went down and didn’t return to base to be counted in the research. The military listened and armoured the engine not the wings and tail.

The US Airforce suffered over 88,000 casualties during the Second World War. Without Wald’s research this undoubtedly would have been higher. But his insight continues to this day and has become an issue in clinical research, financial markets and the people we choose to look up to.

Survivorship Bias in Clinical Research

In 2010 in Boston, Massachusetts a trial was conducted at Harvard Medical School and Beth Israel Deaconess Medical Center (BIDMC) into improving patient survival following trauma. A major problem following trauma is if the patient develops abnormal blood clotting or coagulopathy. This hinders them in stemming any bleeding they have and increases their chances of bleeding to death. Within our blood are naturally occurring proteins called factors which act to encourage blood clotting. The team at Harvard and BIDMC investigated whether giving trauma patients one of these factors would improve survival. The study was aimed at patients who had received 4-8 blood transfusions within 12 hours of their injury. They hoped to recruit 1502 patients but abandoned the trial after recruiting only 573.

Why? Survivorship bias. The trial only included patients who survived their initial accident and then received care in the Emergency Department before going to Intensive Care with enough time passed to have been given at least 4 bags of blood. Those patients who died prior to hospital or in the Emergency Department were not included. The team concluded that due to rising standards in emergency care it was actually very difficult to find patients suitable for the trial. It was therefore pointless to continue with the research.

This research was not the only piece reporting survivorship bias in trauma research. Does this matter? Yes. Trauma is the biggest cause of death worldwide in the under 45 year-olds. About 5.8 million people die worldwide due to trauma. That’s more than the annual total of deaths due to malaria, tuberculosis and HIV/AIDS. Combined. Or, to put it another way, one third of the total number of deaths in combat during the whole of the Second World War. Every year. Anything that impedes research into trauma has to be understood. Otherwise it costs lives. But 90% of injury deaths occur in less economically developed countries. Yet we perform research in Major Trauma Units in the West. Survivorship bias again.

As our understanding of survivorship bias grows so we are realising that no area of Medicine is safe. It clouds outcomes in surgery and anti-microbial research. It touches cancer research. Cancer survival rates are usually expressed as 5 year survival; the percentage of patients alive 5 years after survival. But this doesn’t include the patients who died of something other than cancer and so may be falsely optimistic. However, Medicine is only a part of the human experience survivorship bias touches.

Survivorship Bias in Financial Markets & our Role Models

Between 1950 and 1980 Mexico industrialised at an amazing rate achieving an average of 6.5% growth annually. The ‘Mexico Miracle’ was held up as an example of how to run an economy as well as encouraging investment into Latin American markets. However, since 1980 the miracle has run out and never returned. Again, looking only at the successes and not the failures can cost investors a lot of money.

Say I’m a fund manager and I approach you asking for investment. I quote an average of 1.8% growth across my funds. Sensibly you do your research and request my full portfolio:


It is common practice in the fund market to only quote active funds. Poorly performing funds, especially those with negative growth, are closed. If we only look at my active funds in this example then yes, my average growth is 1.8%. You might invest in me. If however you look at all of my portfolio then actually my average performance is -0.2% growth. You probably wouldn’t invest then.

Yet survivorship bias has a slight less tangible effect on modern life now. How often is Mark Zuckerberg held up as an example for anyone working in business? We focus on the one self-made billionaire who dropped out of education before making their fortune and not the thousands who followed the same path but failed. A single actor or sports star is used as a case study on how to succeed and we are encouraged to follow their path never mind that many who do fail. Think as well about how we look at other aspects of life. How often do we look at one car still in use after 50 years or one building still standing after centuries and say, “we don’t make them like they used to”? We overlook how many cars or buildings of a similar age have now rusted or crumbled away. All of this is the same thought process going through the minds of the US Military as they counted bullet holes in their planes.

To the victor belong the spoils but we must always remember the danger of only looking at the positive outcomes and ignoring those often invisible negatives. We must be aware of the need to see the whole picture and notice when we are not. With our appreciation of survivorship bias must also come an appreciation of Abraham Wald. A man whose simple yet profound insight shows us the value of stepping back and thinking.

Thanks for reading

- Jamie