• Randomised controlled trials (RCTs) are a type of scientific experiment that aim to reduce bias when testing a new treatment or intervention
• In its simplest form, a RCT consists of a control group and a treatment group, with the treatment group randomly receiving the intervention and the control group not receiving it
• They are often used in medicine, psychology, and social sciences to evaluate the effectiveness of new treatments or interventions
• It is easy to take them for granted, but these trials have transformed our understanding of cause and effect
• They are the best tool we have to illuminate what is unknown or uncertain, and to discern whether something works and how well it works

• Petrarch (1394): “I solemnly affirm and believe, if a hundred or a thousand of men of the same age, same temperament and habits, together with the same surroundings, were attacked at the same time by the same disease, that if the one half followed the prescriptions of doctors of the variety of those practicing at the present day, and that the other half took no medicine but relied on Nature’s instincts, I have no doubt as to which half would escape”

• In 1747, Scottish naval surgeon James Lind sought to cure scurvy during a sea voyage
• Lind implemented the first (non-randomised) experiment comparing two treatments across six pairs of sailors
• One effective treatment involved administering two oranges and one lemon daily to sailors
• To ensure consistency, Lind aimed for similarity among participants: “The cases were as similar as I could have them. They all in general had putrid gums, the spots and lassitude, with weakness of their knees. They lay together in one place, being a proper apartment of the sick in the fore-hold; and had one diet common to all.”

• The first random assignment of treatment and control happened in Nuremberg, 1835, to assess homeopathic medicine (yes, it’s been ongoing for a while!)
• In 1884, Peirce and Jastrow conducted the first psychological experiment using randomisation to study sensory perception
• This approach later became standard practice in experimental psychology and social sciences
• In 1947, the Medical Research Council carried out the first RCT to evaluate streptomycin for tuberculosis
• Results showed streptomycin was effective, and the RCT became the gold standard for evaluating medical treatments

• Lab experiments: Conducted in controlled environments
• Field experiments: Conducted in real-world settings
• Natural experiments: Use naturally occurring events as treatments
• Quasi-experiments: Use non-randomised designs

• Why are natural/quasi-experiments not as reliable as RCTs?

• David Hume (1739): “We may define a cause to be an object followed by another, and where all the objects similar to the first are followed by objects similar to the second. Or in other words where, if the first object had not been, the second never had existed.”
• Three concepts worth noting:
  • Temporal sequence: The cause must precede the effect
  • Covariation: The cause and effect must vary together
  • Non-spuriousness: The relationship must not be due to a third variable

• A more modern take involves 5 principles:
  • Relationship: There must be a relationship between the cause and effect
  • Direction (temporality): The cause must precede the effect
  • Nonconfounding: The relationship must not be due to a third variable
  • Mechanism: There must be a plausible mechanism linking the cause and effect
  • Appropriate level of analysis: The relationship must happen (and be measured) at the appropriate level of analysis

Required: Alan Gerber and Donald Green - Field Experiments

Recommended: Douglas C. Montgomery - Design and Analysis of Experiments