# What does exchangeability mean in statistics?

## What does exchangeability mean in statistics?

Exchangeability is meant to capture symmetry in a problem, symmetry in a sense that does not require independence. Formally, a sequence is exchangeable if its joint probability distribution is a symmetric function of its n arguments.

What is exchangeability Bayesian?

Modern Bayesian Inference Formally, this is captured by the notion of exchangeability. The set of random vectors {x1,… ,xn} is exchangeable if their joint distribution is invariant under permutations. An infinite sequence {xj} of random vectors is exchangeable if all its finite subsequences are exchangeable.

Why is exchangeability important?

Exchangability is essential in the sense that these conditional independence relationships allow us to fit models we almost certainly couldn’t otherwise. We make conditional independence assumptions, i.e., conditional on Θ2, the Θ1 are exchangeable.

### What is exchangeability in epidemiology?

Exchangeability occurs when the unexposed group is a good proxy (i.e., approximation) for the disease experience of the exposed group had they not been exposed.

How to explain the concept of’exchangeability’?

1 Answer 1. Exchangeability is meant to capture symmetry in a problem, symmetry in a sense that does not require independence. Formally, a sequence is exchangeable if its joint probability distribution is a symmetric function of its \$n\$ arguments.

How are exchangeable random variables used in statistical models?

It is closely related to the use of independent and identically distributed random variables in statistical models. Exchangeable sequences of random variables arise in cases of simple random sampling .

#### Which is an example of an infinitely exchangeable probability?

P∫ΘPθdμ(θ). That is, every exchangeable P on infinite sequences can be represented as a mixture of independent and identically distributed probabilities. (It is clear that every mixture of iid sequences is exchangeable; it is the point of the representation theorem that conversely every infinitely exchangeable probability arises thus.

Is the covariance of exchangeable random variables fixed?

For finite exchangeable sequences the covariance is also a fixed value which does not depend on the particular random variables in the sequence. There is a weaker lower bound than for infinite exchangeability and it is possible for negative correlation to exist.