Lecture 1
Observation
● Individuals, study subjects participants, units
○ 336,289 US, Swedish, and Australian adults in several studies
● Treatment
○ Chocolate consumption
● Outcome
○ Heart disease
The first question
Is there any relation between chocolate consumption and heart disease?
● Association
○ Any relation
○ Link
Answer: Yes, because those who ate chocolate had less heart disease
The next question:
Does chocolate consumption lead to a reduction in heart disease?
● Causality
This question is often harder to answer
Association
Miasma
● Bad smell given off by waste and rotting matter
● Believed to be a main source of disease
● Believers included:
○ Florence nightingale
○ Edwin Chadwick, Commissioner of the General Board of Health
Suggested Remedies
Cholera around 1850
● Fly to “clene air”
● Fire off barrels of gunpowder
● Fetch clean air from the top of the Eiffel Tower in Paris
Covid19 2020
● Inject disinfectant
● Sunlight
● Hydroxychloroquine
● Take 6 deep breaths, then cough while covering mouth
● Cannabis, cocaine, mangoes, onion, garlic, drinking water every 15 minutes, tea, eating
ice cream, avoiding ice cream
Causation
Comparison
● Treatment group
● Control group
○ Does not receive the treatment
, ● The two groups were similar except for the treatment
If the treatment and control groups are similar apart from the treatment, then differences
between the outcomes in the two groups can be ascribed to the treatment.
Confounding
Trouble
If the treatment and control groups have systematic differences other than the treatment, then it
might be difficult to identify casualty
Such differences are often present in observational studies
When they lead researchers astray, they are called confounding factors
Randomize!
● If you assign individuals to treatment and control at random, then the two groups are
likely to be similar apart from the treatment
● You can account - mathematically - for variability in the assignment
● Randomized Controlled Experiment
Careful
Regardless of what the dictionary says, in probability theory
Randomize ≠ Haphazard
Observation
● Individuals, study subjects participants, units
○ 336,289 US, Swedish, and Australian adults in several studies
● Treatment
○ Chocolate consumption
● Outcome
○ Heart disease
The first question
Is there any relation between chocolate consumption and heart disease?
● Association
○ Any relation
○ Link
Answer: Yes, because those who ate chocolate had less heart disease
The next question:
Does chocolate consumption lead to a reduction in heart disease?
● Causality
This question is often harder to answer
Association
Miasma
● Bad smell given off by waste and rotting matter
● Believed to be a main source of disease
● Believers included:
○ Florence nightingale
○ Edwin Chadwick, Commissioner of the General Board of Health
Suggested Remedies
Cholera around 1850
● Fly to “clene air”
● Fire off barrels of gunpowder
● Fetch clean air from the top of the Eiffel Tower in Paris
Covid19 2020
● Inject disinfectant
● Sunlight
● Hydroxychloroquine
● Take 6 deep breaths, then cough while covering mouth
● Cannabis, cocaine, mangoes, onion, garlic, drinking water every 15 minutes, tea, eating
ice cream, avoiding ice cream
Causation
Comparison
● Treatment group
● Control group
○ Does not receive the treatment
, ● The two groups were similar except for the treatment
If the treatment and control groups are similar apart from the treatment, then differences
between the outcomes in the two groups can be ascribed to the treatment.
Confounding
Trouble
If the treatment and control groups have systematic differences other than the treatment, then it
might be difficult to identify casualty
Such differences are often present in observational studies
When they lead researchers astray, they are called confounding factors
Randomize!
● If you assign individuals to treatment and control at random, then the two groups are
likely to be similar apart from the treatment
● You can account - mathematically - for variability in the assignment
● Randomized Controlled Experiment
Careful
Regardless of what the dictionary says, in probability theory
Randomize ≠ Haphazard
