March 30, 2021
Clinical trials are experiments. Correlation between treatment and health outcomes are causal (do not have confounding) assuming that…
TO THE BOARD
Does the efficacy of vaccines in clinical trials translate to real world use??
Might appear to be the only valid solution:
Experiments, under weak assumptions, let us find an unbiased causal relationship between X and Y
A research design (choice of which cases to compare using correlation) has internal validity when the causal effect of X on Y it finds is not biased (systematically incorrect) / does not suffer from confounding.
What can we manipulate?
Who/what cases can we study?
is the degree to which the causal relationship we find in a study captures/is relevant to the causal relationship in our causal question/claim
Study has external validity if the relationship found is true for the cases we are interested in
Study has external validity if the causal variable in the study maps onto the concept/definition of the cause in the causal claim.
More internal validity (unbiased calculation of causal effect) comes at the cost in external validity (relevance of study sample or cause to the theory)
Before we return to vaccination
You live in mid-19th century London.
What causes the spread of cholera?
Dominant view was that “miasmas” or bad air caused diseases like cholera